Bell Work In a certain set of lab mice, black hair (B) is dominant to white hair (b), & coarse hair (C) is dominant to fine hair (c). In a cross between a heterozygous black, fine-haired mouse and a white heterozygous coarse-haired mouse. What is the probability that this cross will produce black, coarse-haired offspring? a. 2/16 b. 4/16 c. 8/16 d. 10/16

FOIL heterozygous black fine haired mouse = Bbcc White heterozygous coarse-haired mouse = bbCc Bbcc x bbCc Bc, Bc, bc, bc parent 1 bC, bc, bC, bc parent 2

bC bC bc bc Bc bc BbCc Bbcc bbCc bbcc What is the probability that this cross will produce black, coarse haired offspring? 4/16

Section Assessment Question Review In human cells, 2N = 46. How many chromosomes would you expect to find in a 1) sperm cell? 2) egg cell? 3) white blood cell? 23 (gamete) 46 (somatic cell)

Genetics – the study of heredity Who is Gregor Mendel? Gregor Mendel’s experiments with pea plants laid the foundations of the science of genetics. “Father of Genetics”

Traits Genetics – study of how traits are passed from parent to offspring

Traits are determined by the genes on the chromosomes. A gene is a segment of DNA that determines a trait.

Chromosomes come in homologous pairs, thus genes come in pairs. Homologous pairs – matching genes – one from female parent and one from male parent Example: Humans have 46 chromosomes or 23 pairs. One set from dad – 23 in sperm One set from mom – 23 in egg

One pair of Homologous Chromosomes: Gene for eye color (blue eyes) Homologous pair of chromosomes Gene for eye color (brown eyes) Alleles – different genes (possibilities) for the same trait – ex: blue eyes or brown eyes

Dominant and Recessive Genes Gene that prevents the other gene from “showing” – dominant Gene that does NOT “show” even though it is present – recessive Symbol – Dominant gene – upper case letter – B Recessive gene – lower case letter – b Recessive color Dominant color

(Always use the same letter for the same alleles— Example: Straight thumb is dominant to hitchhiker thumb T = straight thumb t = hitchhikers thumb (Always use the same letter for the same alleles— No S = straight, h = hitchhiker’s) Straight thumb = TT Straight thumb = Tt Hitchhikers thumb = tt * Must have 2 recessive alleles for a recessive trait to “show”

Both genes of a pair are the same – homozygous or purebred TT – homozygous dominant tt – homozygous recessive One dominant and one recessive gene – heterozygous or hybrid Tt – heterozygous BB – Black Bb – Black w/ white gene bb – White

Genotype and Phenotype Combination of genes an organism has (actual gene makeup) – genotype Ex: TT, Tt, tt Physical appearance resulting from gene make-up – phenotype Ex: hitchhiker’s thumb or straight thumb

Punnett Square and Probability Used to predict the possible gene makeup of offspring – Punnett Square Example: Black fur (B) is dominant to white fur (b) in mice Cross a heterozygous male with a homozygous recessive female. Black fur (B) White fur (b) Heterozygous male Homozygous recessive female White fur (b) White fur (b)

Male = Bb x Female = bb Bb b B bb Female gametes – N (One gene in egg) Possible offspring – 2N Male gametes - N (One gene in sperm) Genotypic ratio = 2 Bb : 2 bb 50% Bb : 50% bb Phenotypic ratio = 2 black : 2 white 50% black : 50% white

Cross 2 hybrid mice and give the genotypic ratio and phenotypic ratio. Bb X Bb B b BB Bb bb B b Genotypic ratio = 1 BB : 2 Bb : 1 bb 25% BB : 50% Bb : 25% bb Phenotypic ratio = 3 black : 1 white 75% black : 25% white

Sex Determination Humans have 46 chromosomes (or 23 pairs) 22 pairs are homologous (look alike) - called autosomes – determine body traits 1 pair = the sex chromosomes & determines sex Female – sex chromosomes are homologous XX Male- sex chromosomes are different XY

What is the probability of a couple having a boy? Or a girl? Chance of having female baby? 50% male baby? 50% X X XX XY X Y Who determines the sex of the child? father

Beyond Dominant & Recessive Alleles Not all genes show simple patterns of dominant and recessive alleles. Also, many traits are controlled by multiple alleles or multiple genes. In most organisms, genetics is more complicated due to circumstances such as: incomplete dominance codominance multiple alleles polygenic traits

R r RR Rr rr R r Incomplete dominance When one allele is NOT completely dominant over another (they blend) – incomplete dominance Example: In four o’clock flowers, the color red (R) is incompletely dominant over white (r). The hybrid color is pink. Give the genotypic and phenotypic ratio from a cross between 2 pink flowers. Rr X Rr R r RR Rr rr R r Genotypic = 1 RR : 2 Rr : 1 rr Phenotypic = 1 red : 2 pink : 1 white

CODOMINANCE When both alleles are expressed – Codominance Example: In certain chickens black feathers are codominant with white feathers. Heterozygous chickens have black and white speckled feathers.

Polygenic Traits - produced by the interaction of several genes Polygenic Traits - produced by the interaction of several genes. Example: height and skin color in humans

Multiple Alleles 3 or more alleles of the same gene that code for a single trait In humans, blood type is determined by 3 alleles A, B, and O Blood Types AA, AO = type A BB, BO = type B AB = type AB OO = type O

Children would be type A or B only Example: What would be the possible blood types of children born to a female with type AB blood and a male with type O blood? AB X OO A B AO BO O O Children would be type A or B only

In eukaryotic organisms, cells grow and divide in two ways: either by mitosis or meiosis. When you scrape your arm, your cells divide and go through _____________. MITOSIS During the formation of gametes, the cells divide and go through _____________. MEIOSIS

Chapter 10 Review - MITOSIS Mitosis- the division of body cells (SOMATIC) The Cell Cycle Interphase (G1, S, G2) Mitosis (PMAT) – division of the nucleus Cytokinesis - division of the cytoplasm

Interphase- G1 & G2 are growth phases S phase = synthesis Interphase- G1 & G2 are growth phases S phase = synthesis ** the DNA is replicated during the S phase** There are checkpoints in the Cell Cycle to ensure proper division of the cell

The chromosomes condense & become visible PMAT = Prophase, Metaphase, Anaphase, Telophase Prophase The chromosomes condense & become visible The centrioles move towards opposite sides of the cell The nuclear membrane dissolves The mitotic spindle forms (form the centrioles)

PMAT = Prophase, Metaphase, Anaphase, Telophase The centrioles complete their migration to each side of the cell The chromosomes line up in the middle of the cell

PMAT = Prophase, Metaphase, Anaphase, Telophase Spindle fibers continue to shorten, pulling chromatids to opposite poles. This ensures that each daughter cell gets identical sets of chromosomes

Telophase PMAT = Prophase, Metaphase, Anaphase, Telophase The chromosomes decondense The nuclear envelope forms Cytokinesis reaches completion, creating two daughter cells

Mitosis in a plant cell

Mitosis vs. Meiosis Mitosis results in the production of two genetically identical diploid (2N) cells (somatic) A CELL THAT CONTAINS BOTH SETS OF HOMOLOGOUS CHROMOSOMES = DIPLOID. Meiosis produces four genetically different haploid cells (gametes) (N). A CELL THAT CONTAINS ONLY A SINGLE SET OF CHROMOSOMES, THEREFORE ONLY A SINGLE SET OF GENES = HAPLOID.

What makes each cell different? As homologous chromosomes pair up and form tetrads in meiosis I, they exchange portions of their chromatids in a process called CROSSING-OVER. Crossing-over results in the exchange of alleles between homologous chromosomes and produces new combinations of alleles.

Meiosis two distinct divisions called Meiosis I and Meiosis II During Meiosis, the number of chromosomes per cell is cut in half through the separation of the homologous chromosomes. The result of Meiosis is 4 haploid cells that are genetically different from one another and from the original cell.

Chapter 11 Review/ Vocab Worksheet If peas are __, it means that if they were allowed to self-pollinate, they would produce identical offspring. True-Breeding 2. Different forms of genes are known as ___ alleles

3. For the characteristic of tallness label the dominant allele and the recessive allele: T = dominant t = recessive 4. Which of the following is heterozygous? Tt 5. Write the genotype for homozygous dominant yellow plant: YY

6. What happens to the phenotype of the offspring when a homozygous tall pea plant and a homozygous short pea plant are crossed? all appear tall; it appears as if the short trait disappeared; Tt 7. The offspring of crosses between parents with different traits are called _____. hybrids

8. Mendel suggested that alleles for tallness or shortness in the F1 plants segregated from each other during the formation of sex cells, or ____. gametes 9. The likelihood that a particular event will occur is called ____. probability 10. The probable gene combinations that might result from a genetic cross can be determined by drawing a diagram called a ____ punnett square

11. The principle of ___ states that genes for different traits can segregate independently during the formation of gametes. independent assortment 12. True or False: Not all genes show simple patterns of dominant and recessive alleles. True 13. A situation in which a gene has more than two allele (possibilities) is called ___ multiple alleles

14. A cross in which the heterozygous phenotype is a blend between the two homozygous phenotypes: __ incomplete dominance 15. In ____ both alleles contribute to the phenotype. codominance 16. What are all the possible alleles for the four blood types? AA, AO BB, BO AB OO

Vocabulary Review Heterozygous Parent Heterozygous offspring Homozygous offspring Recessive allele Dominant allele

7. C 8. E 9. H 10. A 11. D 12. B 13. F 14. I 15. G

16. The process in which two genes segregate independently is called ___ independent assortment 17. Plants that, if left to self-pollinate, produce offspring identical to themselves are called __ true-breeding 18. The offspring crosses between parents with different traits are called ____ hybrids

19. The process during sexual reproduction in which male and female sex cells join is called fertilization 20. The process of reduction division in which the number of chromosomes per cell is cut in half is called ___ meiosis