Mendel and Meiosis Chapter 10

Mendel’s Laws of Heredity Heredity- Passing on of characteristics from parents to offspring.   TRAITS- Characteristics that are inherited.    Genetics- STUDY OF HEREDITY GREGOR MENDEL was the first to succeed in predicting how traits are transferred from one generation to the next.

GARDEN PEA EXPERIMENT Mendel used garden peas to conduct his experiments because: 1.REPRODUCE SEXUALLY (they produce male and female sex cells called _GAMETES) a. male gamete forms in the pollen grain. SPERM or male sex cell b. female gamete forms in female reproductive organ. OVUM or female sex cell.   In fertilization the female gamete (ovum) unites with the male gamete (sperm) to form a ZYGOTE which develops into a seed. 2. In pea plants both female and male organs are in the same plant and tightly enclosed by petals, which prevents other pollens form entering. - Reproduction is PURE AND CONTROLLED

TYPICAL FLOWER

How he did it: Mendel’s Experiment (fig 10.1) -Removed male organ -dusted pollen of his choice on female organ CROSSPOLLINATION. -Sure of what he crossed -Well CONTROLLED experiment -Studied ONE trait at a time. -Analyzed data MATHEMATICALLY.

FLOWER POLLINATION

MONOHYBRID CROSS HYBRID offspring of parents that have a different form of a trait For example: short x tall MONOHYBRID cross means that he crossed plants that differed in only ONE trait. What do you get when you cross a gas powered car with and electric car?

Monohybrid Punnet squares Original Parents : P1 1st generation: F1 (F=filial meaning son or daughters) 2nd generation: F2 RR x rr = F 1 Rr x Rr = F 2 Mendel eventually studied 7 traits

Mendel’s rules Rule of Unit Factors: Each organism has 2 factors that control each of its traits. Genes exist in alternative forms called ALLELES 2 alleles determine one trait. (Tt) Recessive trait only when tt. Is present

Rule of dominance Rule of dominance- One trait is dominant over another. The trait is expressed as long as it is present in the gene TT or Tt.

Law of segregation Every individual has 2 alleles for each gene and when gametes are produced each gamete only receives one of these alleles. During fertilization these gametes randomly pair to produce 4 combinations

PHENOTYPE The way an organism looks and behaves PHENOTYPE The way an organism looks and behaves. (may have environmental influence)   GENOTYPE- The actual allele make up of the organism. HOMOZYGOUS traits have the same 2 alleles for a trait. ( TT or tt) HETEROZYGOUS traits have 2 different alleles for a trait. (Tt) 

DIHYBRID CROSSES-crossing two traits at once Law of independent assortment- Genes for different traits are inherited independently of one another,

SEXUAL REPRODUCTION SECTION 2 A cell with 2 of each kind of Chromosome is called a DIPLOID cell or contains 2n for the # of chromosomes. A cell that produces gametes (sex cells- ovum and sperm cells), contain one kind of each chromosome know and a HAPLOID or n number of chromosomes.   Two chromosomes with identical information are called homologous chromosomes. They are similar structures. They contain the genes for a specific trait, ex. Height. Genes are arranged in the same order but because there are different alleles (dominant and recessive) they may not be identical.

Problem solving lab 10.2

Sex linked traits Traits controlled by genes located on the X and Y chromosome. Because X and Y are not homologus they do not carry the corresponding allele to each other. Characteristics carried on X will be expressed and not masked by the other chromosome. Examples: Male pattern baldness, red-green color blindness, hemophilia (X-linked)

Co-dominant Traits Human traits are often complicated and not expressed purely as either dominant or recessive but rather a mixture of the two traits. Incomplete dominance For example: Sickle cell anemia (blood disorder that effects African American population), blood types

Recessive Heredity Cystic Fibrosis- White Americans Tay-Sachs disease- Ashkenasic Jews Phenylketonuria (PKU)- Tested for at birth Lesch Nyhan

Dominant Heredity Cleft chin Hitchhikers thumb Attached earlobe Huntington’s disease- 30-50yoa is expressed.

MEIOSIS If cells reprduced gametes with a complete set of chromosomes (for example 14 chromosomes /7 pairs) each generation would double chromosomes. F2- 28 chromosomes 14 pairs F3- 56 chromosomes 28 pairs F4- 102 chromosomes 56 pairs F5- 204 chromosomes or 102 pairs!!!

MEIOSIS MEIOSIS is cell division that results in HALF the number of chromosomes as the parent’s body cell.   Male gamete= SPERM Female gamete= EGGS When the sperm cell fertilizes the egg the result is a ZYGOTE with a diploid # of chromosomes.  

PHASES OF MEIOSIS Interphase: Same as mitosis. 1.PROPHASE I DNA coils, homologous chromosomes line up. Spindle forms HOMOLOGOUS structure forms called a TETRAD each made of 2 sister chromatids. ( some crossing over occurs causing an exchange of DNA information.)

Prophase 1 cont… Chromosomes in a tetrad pair so tightly that non sister chromatids can actually break and exchange material. This is called Crossing over.

2.METAPHASE I Pulled to equator like in Mitosis except the tetrad structure is side by side.

Meiosis I cont… 3.Anaphase I 4.Telophase I Homologous chromosomes separate (tetrad pair separate) Ensures each new cell will only receive one of the homologous chromosomes. 4.Telophase I New cells appear with full set of genetic information. One homologous pair in each cell.

Meiosis II Some cells undergo a short resting phase, others go directly into meiosis II. It is simply mitosis. Prophase II Spindle forms and attach to chromosomes Metaphase II Sister Chromatids line up at equator Anaphase II Centromere splits apart and sister chromatids separate and move to opposite poles. Telophase II Nuclei reform, spindles break down   CYTOKINESIS – finishes process

Meiosis II  Same as mitosis EXCEPT chromosomes DO NOT REPLICATE before they divide. 4 HAPLOID cells result.

Genetic variation Since each pair can line up at the equator 2 different ways there are a 2N or 2 46 or 7 x1013 or 70, 400, 000,000,000 possibilities, or 70 trillion possibilities. Genetic recombination- reassortment of chromosomes and the genetic information they carry.

Genetic alterations Nondisjunction: Gamete missing : Turner Female XO Failure of chromosomes to SEPARATE properly.   Ex. Extra chromosomes in one cell or missing one in another. Down’s Syndrome is Trisomy 21. Gamete missing : Turner Female XO Tetraploid: 2 complete sets of chromosomes Polyploidy- Organisms with more than the usual # of chromosomes. Death of zygote in animal cells. Common in plants through genetic engineering.

Karyotype