1. SEXUAL REPRODUCTION AND GENETICS
CHAPTER 10
SEXUAL REPRODUCTION AND GENETICS

2. SECTION 10.1 – MEIOSIS
MAIN IDEA – MEIOSIS PRODUCES HAPLOID GAMETES.
All of the differences you see in the room, different hair color, eye color, ear shapes, is the result of 2 sex cells combining during sexual reproduction.
QUESTION: How are the following cell parts involved in mitosis?
Chromosome, spindle fibers, nucleus, and nucleolus

3. CHROMOSOMES AND CHROMOSOME NUMBER
Everyone has characteristics passed on to them from their parents.
Each characteristic is called a trait.
Ex: hair color, height or eye color
The instructions for each trait are located on the chromosomes, which are found in the nucleus of cells.
The DNA on the chromosomes is arranged in segments called genes that control the production of proteins.
Each chromosome has 100’s of genes.

4. HOMOLOGOUS CHROMOSOMES
Human body cells (somatic cells) have 46 chromosomes.
Each parent gave you 23 chromosomes creating 23 PAIRS of chromosomes or 46 chromosomes.
The chromosomes that make up a pair (the one from mom & the one from dad) are called homologous chromosomes
Homologous chromosomes in body cells have the same length, same centromere position, and carry genes that control the same inherited traits.
These genes each code for the same trait (ex: earlobe) but maybe not the same type of trait (earlobe)

5. HAPLOID AND DIPLOID CELLS
Gametes are sex cells that have half the number of chromosomes.
In humans the number of chromosomes in a gamete is 23.
Each species has a different # of chromosomes
The symbol n can be used to represent the number of chromosomes in a gamete.
Cells with n number of chromosomes is called a haploid cell.
Haploos means single.
Fertilization is the process by which one haploid gamete (egg) combines with another haploid gamete (sperm)
Fertilization creates cells that are 2n (one n chromosome from mom & one n chromosome from dad)
2n cells are called diploid cells

6. MEIOSIS I
Gametes are formed during a process called meiosis.
Meiosis is a type of cell division that reduces the number of chromosomes
Meiosis is a reduction division.
Mitosis maintains the chromosome #, meiosis reduces the chromosome # by half through the separation of homologous chromosomes.
Cells begin as 2n, but create gametes with n number of chromosomes
Meiosis occurs in the reproductive structures of organisms that reproduce sexually.
Meiosis involves 2 consecutive cell divisions called meiosis I & meiosis II

7. INTERPHASE
Just like with mitosis, cells that undergo meiosis also go through interphase as part of their cell cycle.
While in interphase cells carry out various metabolic processes, including the replication of DNA and the synthesis of proteins

8. PROPHASE I
Cells entering prophase I, the replicated (copied) chromosomes become visible.
Creating sister chromatids
Homologous chromosomes (mom’s sister chromatid + dad’s sister chromatid) form during synapsis and are held tightly together. Can be called a tetrad.
Crossing over occurs this time.
Crossing over is a process when segments of chromosomes are exchanged between a pair of homologous chromosomes.
Prophase I continues with the centrioles moving to the cell’s opposite poles, spindle fibers forming and binding to the sister chromatids at the centromere.

9. PROPHASE I

10. METAPHASE I
2nd phase of meiosis
Homologous chromosomes line up at the equator of the cell.
Spindle fibers are attached to the centromere of each homologous chromosome

11. ANAPHASE I
During anaphase I homologous chromosomes separate.
Sister chromatids are pulled to opposite poles of the cell
Chromosome number is reduced from 2n to n when the homologous chromosomes separate.

12. TELOPHASE I
Homologous chromosomes (sister chromatids) reach the cell’s opposite poles.
Sister chromatids are still joined at the centromere
Sister chromatids might not be identical from when it started because of crossing over.
During telophase I, cytokinesis usually occurs pinching in the animal cell or forming cell plate in plant cells.
May or may not go into interphase. If cell goes into interphase, DNA is NOT duplicated again.

13. Telophase I

14. MEIOSIS II
Meiosis is only half done after meiosis I.
Prophase II the sister chromatids condense and spindle apparatus forms
Metaphase II the sister chromatids line up at the equator by the spindle fibers.
Anaphase II the sister chromatids are pulled apart at the centromere by the spindle fibers and the chromosomes move toward the opposite poles of the cell.
Telophase II the chromosomes reach the poles and the nuclear membrane and nuclei reform.
At the end of meiosis II, cytokinesis occurs creating 4 haploid cells each with n number of chromosomes

15. MEIOSIS II

16. MEIOSIS PROVIDES VARIATION
Genetic variation is produced during crossing over and during fertilization when gametes randomly combine.
Depending on how chromosomes line up at the equator, 4 gametes with 4 different combinations of chromosomes can result.
SEXUAL REPRODUCTION VS. ASEXUAL REPRODUCTION
Asexual reproduction the organism inherits all of its chromosomes from a single parent and are genetically identical to the parent.
Ex: bacteria
Sexual reproduction allows variation and beneficial mutations to accumulate faster in the population.

17. SECTION 10.2 – MENDELIAN GENETICS
MAIN IDEA – Mendel explained how a dominant allele can mask the presence of a recessive allele.
QUESTION: Do all dogs look alike?
What types of features indicate a particular breed?
Are these features inherited?
What does this tell you about the inheritance of these features?

18. HOW GENETICS BEGAN
In 1866 Gregor Mendel, an Austrian monk, published a book on the method of inheritance in garden pea plants.
Inheritance or heredity is the passing of traits from one generation to the next.
Mendel chose pea plants to study because they are true-breeding, meaning that they consistently produce offspring with only one form of a trait.
EX: always purple flowers
Pea plants self-pollinate, but Mendel began to cross-pollinate the pea plants.

19. THE INHERITANCE OF TRAITS
Mendel noticed that some varieties of peas produced a specific form of a trait generation after generation.
EX: always green seeds or yellow seeds
Mendel cross-pollinated (male gamete of one plant & combined with female gamete of the other plant)
Mendel referred to the male gamete & female gametes used in the cross-pollination as the P generation or the parent generation.

20. F1 AND F2 GENERATION
Mendel grew the seeds from the cross from the parent generation (P generation), one green seed and one yellow seed and the results were all the offspring had yellow seeds.
The offspring from the parent generation (P generation) are called the F1 generation or first filial generation.
Mendel questioned if the green seed was gone or being hidden or masked.
Mendel planted the F1 generation and allowed them to self-pollinate and then examined the seeds from this cross.
The offspring from the F1 generation is called the F2 generation or second filial generation.
Mendel’s results were a 3:1 ratio of 6022 yellow seeds to 2001 green seeds

21. GENES IN PAIRS
Mendel concluded there must be 2 forms of the seed trait in pea plants – yellow and green seeds.
Allele is an alternative form of a single gene passed from generation to generation.
Gene for yellow seeds and the gene for green seeds are each different forms (alleles) of a single gene.
In Mendel’s experiments the yellow seed color was dominant over the recessive green seed color.
Reason why the F1 generation was yellow and explaining why the F2 generation had the 3:1 ratio of yellow to green

22. DOMINANCE
When the dominant allele is present it will be the one that is shown.
Ex: Yellow seeds are dominant over the green seeds, results shown in the F1 generation cross that Mendel made
When modeling inheritance, the dominant allele is represented by a capital letter.
The letter used is the beginning letter of the dominant trait.
Ex: Yellow seeds used the capital Y
Ex: Round seeds dominant use capital letter R
When modeling inheritance, the recessive allele is represented by a lower case letter.
Homozygous for a particular trait means that the organism has the same 2 alleles.
Ex: homozygous (dominant) yellow seeds = YY
EX: homozygous (recessive) green seeds = yy

23. DOMINANCE – CONTINUED
Heterozygous for a particular trait means that the organism has 2 different alleles.
EX: one yellow allele and one green allele = Yy
The dominant allele will always be expressed when the organism is heterozygous

24. GENOTYPE AND PHENOTYPE
Genotype is the organisms allele pairs.
Ex: YY is the genotype for homozygous dominant yellow seeds
Ex: Yy is the genotype for heterozygous yellow seeds
EX: yy is the genotype for homozygous recessive green seeds
Phenotype is the observable characteristic or outward expression of an allele pair.
Ex: yellow seeds or green seeds

25. MENDEL’S LAW OF SEGREGATION
Mendel’s Law of Segregation states that the 2 alleles for each trait separate during meiosis.
During fertilization the 2 alleles for that trait unite.
Hybrids are heterozygous organisms.

26. LAW OF INDEPENDENT ASSORTMENT
Law of independent assortment states that a random distribution of alleles occurs during gamete formation. Genes on separate chromosomes sort independently during meiosis.
Ex: an organism heterozygous for seed color (Yy) crossed with another heterozygous organism (Yy) means that the Y allele and the y alleles from both organisms can recombine in any combination.
Either YY, Yy or yy

27. PUNNETT SQUARES
Punnett squares are used to predict the possible offspring of a cross between 2 known genotypes.
PUNNETT SQUARE – MONOHYBRID CROSS
The number of squares is determined by the number of types of alleles produced by each parent.
Male gametes are written across the horizontal side.
Female gametes are written on the vertical side of the Punnett square.
Possible combinations of each male and female gamete are written on the inside of each corresponding square.
Dominant allele is written first, whether it comes from the male or female gamete.

28. PUNNETT SQUARE
Cross between heterozygous male (Bb) and a heterozygous female (B)

29. PUNNETT SQUARE – DIHYBRID CROSS
Dihybrid crosses is when we look at the inheritance of 2 traits at the same time.
Ex: pea plants with yellow seeds (1trait) and round seeds (1 trait)
If Mendel started with homozygous yellow round seeds plant and green wrinkled seeds the F1 generation would be represented by YyRr
Crossing the F1 generation yields a 9:3:3:1 ratio

30. PUNNETT SQUARE – DIHYBRID CROSS

31. PROBABILITY
The inheritance of genes can be compared to the probability of flipping a coin.
Probability of the coin landing on heads is 50% or half the time.
Large number of results makes it more likely that the results will match the predicted results of the Punnett square

32. SECTION 10.3 – GENE LINKAGE & POLYPLOIDY
READ & TAKE NOTES OVER PAGES 283, 284, & 285.
BE PREPARED TO SHARE YOUR NOTES WITH THE CLASS
BE PREPARED TO TAKE A SHORT QUIZ OVER THESE PAGES