1. Chapter 11- Genetics Meiosis Principles of genetics require:
-each organism inherits a single copy of every gene from each parent
-during gamete formation, two sets of genes must separate, so each gamete contains just one set of genes

2. Chapter 11- Genetics Chromosome Number Fruit fly example:
8 chromosomes total
4 came from male parent
4 came from female parent
Two sets are homologous

3. Chapter 11- Genetics
Homologous chromosomes- paired chromosomes having genes for the same trait located at the same place on the chromosome
Diploid- having two of each kind of chromosome (2n); normal body cells
Diploid cells have two complete sets of chromosomes/two complete set of genes

4. Chapter 11- Genetics
Gametes of sexually reproducing organisms have only a single set of chromosomes
Haploid- having one of each kind of chromosome (n)
Fruit fly gametes would be n = 4

6. Chapter 11- Genetics Phases of Meiosis
How haploid cells (gametes) produced from diploid cells (somatic cells)
Meiosis- cell division that results in a gamete containing half the number (n) of chromosomes of its parent (2n)
Involves two rounds of division:
-Meiosis I
-Meiosis II

8. Chapter 11- Genetics Phases of Meiosis Meiosis I Similar to mitosis
Four phases the same: prophase I, metaphase I, anaphase I, and telophase I

9. Chapter 11- Genetics Differences- Prophase I:
Pairing of homologous chromosomes to form tetrad (4 chromatids)
Crossing over- exchange of genetic material between non-sister chromatids of homologous chromosomes
Shuffles genes like a deck of cards

11. Chapter 11- Genetics Meiosis II Second round of division (reduction)
NO chromosome replication
Phases just like meiosis I:
Prophase II, metaphase II, anaphase II, telophase II
At end of division cycle, each cell contains haploid # of chromosomes (n)

12. Chapter 11- Genetics Gamete Formation
In male animals, gametes produced through meiosis called sperm
In some plants, pollen contains sperm cells
In female animals, only one cell produced is made into a gamete
Cytokinesis is uneven: produces one egg and 3 polar bodies

13. Chapter 11- Genetics Comparing Mitosis & Meiosis Mitosis Meiosis
2 identical diploid cells
4 genetically different haploid cells
Multicellular organisms: growth & repair
Formation of gametes
Asexual reproduction
Sexual reproduction

14. Chapter 11- Genetics The Work of Gregor Mendel
Genetics- scientific study of heredity
Gregor Mendel- Austrian monk who experimented using pea plants
Determined rules of inheritance
Fertilization- joining of male & female gametes to form single cell

15. Chapter 11- Genetics Pea plants normally self-pollinating
Mendel used stock of true-breeding plants
(produced offspring identical to themselves)
Cross-pollinated pea plants with different traits to study resulting offspring

16. Chapter 11- Genetics Genes & Dominance
Studied 7 different pea plant traits
Trait- a characteristic that can be passed on to offspring
For each trait, studied a contrasting character:
Ex. Seed color- green or yellow

18. Chapter 11- Genetics Original pair of plants = P generation
Offspring = F1 generation
Hybrid- offspring of parents that have different forms of a trait
Results?
Every offspring had a character of only one of the parents

20. Chapter 11- Genetics Two conclusions:
Inheritance determined by factors passed from one generation to the next
Gene- the functional units of inheritance
Each trait controlled by one gene with two contrasting forms
Alleles- alternate forms of a gene

22. Chapter 11- Genetics
Second conclusion called the principle of dominance:
Some alleles are dominant and others are recessive
Dominant- an allele of a gene that is always expressed (T)
Recessive- an allele of a gene that is expressed only when the dominant allele is not present (t)

23. Chapter 11- Genetics Segregation
What had happened to recessive alleles (traits) in plants?
Mendel allowed F1 plants to self-pollinate
Produced F2 generation which showed recessive trait in 1 out of 4 plants (3:1 ratio)

25. Chapter 11- Genetics
Dominant allele masked recessive trait in F1 generation
Reappearance in F2 generation showed that at some point alleles became separated
Mendel suggested that they segregated from one another during gamete formation

27. Chapter 11- Genetics
Law of Segregation- states that every individual has two alleles of every gene;
when gametes are produced, each gamete receives one of these alleles

28. Chapter 11- Genetics Probability & Punnett Squares
Every time Mendel repeated a particular cross, he obtained similar results
¾ plants showed dominant trait; ¼ showed recessive trait
Mendel realized that probability could be used to explain results

29. Chapter 11- Genetics

30. Chapter 11- Genetics

31. Chapter 11- Genetics Genetics & Probability
Probability- the likelihood that a particular event will occur
Two possible outcomes for a coin flip:
heads or tails
Probability of each occurring is equal
Chance of heads is 1 in 2, or 50%

32. Chapter 11- Genetics Chance of heads coming up three in a row?
Each flip is an independent event:
Probability of three heads in a row-
½ x ½ x ½ = 1/8
Way alleles segregate is random, like a coin flip
Principles of probability can be used to predict outcomes of genetic crosses

33. Chapter 11- Genetics Punnett Squares
Gene combinations from a given cross can be determined using a Punnett square
Letters in Punnett square represent alleles
Gametes from each parent are shown along one side and the top of the square
Used to predict and compare genetic variations resulting from a cross

35. Chapter 11- Genetics
Homozygous- if an organisms two alleles for a trait are the same
Can be homozygous dominant (TT) or homozygous recessive (tt)
Heterozygous- when the two alleles for the same trait are different (Tt)
Homozygous = true-breeding for trait
Heterozygous = hybrid for trait

36. Chapter 11- Genetics
Phenotype- the physical expression of the genes; how the trait looks
Ex.-
Tall; short; yellow seeds; green seeds
Genotype- allele combination that an organism contains
TT; Tt; tt

37. Chapter 11- Genetics Probability & Segregation
Probability predicts that if the alleles segregate, then a 3:1 phenotypic ratio should be seen
Each cross showed a 3:1 ratio
Mendel’s law of segregation proven correct

38. Chapter 11- Genetics Since probabilities predict averages:
the larger the number of individuals, the closer the data comes to the probability

39. Chapter 11- Genetics Exploring Mendelian Genetics
Mendel further investigated:
Alleles segregate-
but do alleles package together?
or are they independent of one another?

40. Chapter 11- Genetics Independent Assortment
Mendel followed two different genes through two generations
Crossed purebred plants for seed color and seed shape
Round, yellow seeds (RRYY)
with
Wrinkled, green seeds (rryy)

41. Chapter 11- Genetics Only provided hybrid plants needed for next cross
All F1 plants had genotype RrYy
F2 generation showed 209 plants that had phenotypes not found in the parents
So…
Alleles for different traits segregate independently of one another

43. Chapter 11- Genetics Summary of Mendel’s Principles
Inheritance is determined by individual units called genes.
Genes passed from parents to offspring.
When two or more forms (alleles) of a gene exist, some forms may be dominant, others recessive.

44. Chapter 11- Genetics
In most sexually reproducing organisms, each adult has two copies of each gene – one from each parent.
These copies are segregated from one another during meiosis (gamete formation)
Alleles for different genes usually segregate independently of one another

45. Chapter 11- Genetics Complex patterns of Inheritance
Important exceptions to Mendel’s principles
Some alleles are neither dominant nor recessive
Many traits controlled by multiple alleles, or multiple genes

46. Chapter 11- Genetics Incomplete dominance
Appearance of a third phenotype
Due to one allele being not completely dominant over another
3rd phenotype somewhere in between the two homozygous phenotypes

48. Chapter 11- Genetics Codominance Expression of both alleles
(ex. White bull crossed with a red cow yields a roan calf)
Both alleles contribute to the phenotype

49. Chapter 11- Genetics Multiple phenotypes from multiple alleles
More common for multiple alleles to control a trait in a population
Only two alleles of a gene can exist within the cell
Multiple alleles for a single gene can be found within a population
Examples:
Blood type- A, B, o
Rabbit coat color- C, cch, ch, c

51. Chapter 11- Genetics Polygenic Inheritance
Traits that are determined through expression of two or more genes
Polygenic traits show wide range of phenotypes
Ex- eye color, skin color, height

54. Chapter 11- Genetics Genetics & the Environment
Characteristics of any organism not solely determined by genes
Determined by interaction between genes and environment
Genes provide plan, how plan goes also depends on environment