Dominance and Punnett Practice Complete Dominance Gray fur is dominant (G) to orange fur (g). Just like the Punnett squares we have been practicing.

Incomplete Dominance The two alleles “blend” together to create a combination of the traits

Co-Dominance Both alleles are shown in the phenotype. One is NOT dominant over the other.

Sex Linked Traits Because the gene controlling the trait is located on the sex chromosome, It is linked to the gender of the individual. Usually found on the X chromosome. The result is that females will have two copies of the sex-linked gene while males will only have one copy of this gene. If the gene is recessive, then males only need one recessive gene to have a sex-link trait. Examples of Sex-linked Traits: Red-green colorblindness Male Pattern Baldness Hemophilia Duchenne Muscular Dystrophy

Dominant vs. Recessive Genotype= the alleles that you have for a trait Phenotype= the physical expression of those alleles A person with a dimpled chin can have the genotype DD or Dd A person with a non-dimpled chin can only have the genotype dd

Homozygous= two of same allele (DD or dd) More Definitions Homozygous= two of same allele (DD or dd) Heterozygous= two different alleles (Dd- also called hybrid)

46 total chromosomes, 23 pairs Human Chromosomes 46 total chromosomes, 23 pairs 23rd pair = sex chromosomes (female = XX , male = XY) The other 22 pairs are called autosomes ALL egg cells carry a single X; sperm carry either an X or a Y This means a woman can ONLY give an X chromosome, a man has a 50/50 chance of giving an X or a Y

Meiosis Meiosis is the process of making gametes (sperm and eggs) Gametes have half the number (23) of chromosomes of the original cells (46) Meiosis turns one 46 chromosome cell into four 23 chromosome cells

Meiosis: How it Happens 23 46 Chrom 23 46 Chrom 92 Chrom Interphase (Double Chromosomes) 46 Chrom 23 Meiosis I 23 Meiosis II

After Meiosis A sperm cell and egg cell, each with 23 chrom., fertilize to form a zygote. + = The cell of the zygote divides/grows to become an embryo, and eventually a baby! The zygote has 46 chromosomes! 23 23

You must half the number of chromosomes to get sperm + egg = 46! Muy Importante! Meiosis is necessary because if you merged two cells with 46 chromosomes each to make a baby, you would get a 92 chromosome mutant! You must half the number of chromosomes to get sperm + egg = 46!

Why Meiosis? Evolutionary Advantage Sexual reproduction increases the genetic variety in a population Greater variety = stronger population Sexual reproduction always involves the combining of genes from two different organisms to form a zygote Plants, animals, fungi, protists…

Asexual Reproduction Asexual reproduction also exists in simple organisms, but makes a clone of the parent This DOES NOT increase genetic variety Some organisms do both types of reproduction Potatoes form sprouts that are clones of themselves. They can also make seeds/sperm to reproduce with neighboring plants.