Bell Work 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? 1)23 (gamete) 2)23 (gamete) 3)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

Gene for eye color (blue eyes) Gene for eye color (brown eyes) Homologous pair of chromosomes One pair of Homologous Chromosomes: 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 Dominant color Recessive color

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

White fur (b) 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 1.Cross a heterozygous male with a homozygous recessive female. Black fur (B) White fur (b) Heterozygous male White fur (b) Homozygous recessive female

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

BBBb bb Bb 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 Cross 2 hybrid mice and give the genotypic ratio and phenotypic ratio. Bb X Bb b

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

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

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

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 RRRr rr R r 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. 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

AB 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 AOBO AOBO 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 ** the DNA is replicated during the S phase** There are checkpoints in the Cell Cycle to ensure proper division of the cell

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 Metaphase 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 Anaphase PMAT = Prophase, Metaphase, Anaphase, Telophase

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

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.

TEST THURSDAY FEBRUARY 18 th Tomorrow– Bring your phones!! Kahoot Test Review Extra Credit- Draw & Describe Meiosis Figure (green box) on page