Unit 5 Meiosis & Heredity

Somatic cells

are any cells in the body that are not involved in reproduction. They make up most of the body's tissues and organs. 2n = 46, every somatic cell has n = 23 pairs of homologous chromosomes

autosomes

chromosomes that do not determine sex. humans have 22 pairs

crossing over

source of genetic variation in which chromosomes exchange genetic material. happens during prophase 1

independent assortment of chromosomes

homologous pairs aline randomly to determine traits. metaphase 1

random fertilization

any sperm and any egg

Law of Segregation

states that allele pairs separate during gamete formation, ensuring that each gamete carries only one allele for each gene.

Law of Independent Assortment

homologous chromosomes separate independently from each other, dependent on how they align at the metaphase plate

complete dominance

heterozygote and homozygote are indistinguishable. Ex. Y/Y or Yy = yellow

incomplete dominance

F₁ hybrids have appearance that is between of 2 parents. Ex. red x white = pink 3 phenotypes

codominance

phenotype of both alleles expressed. Ex. black chicken, white chicken, and speckled chicken

pleiotrophy

one gene has multiple phenotypic effects. Ex. Cystic fibrosis one gene affecting multiple symptoms, Albinism causes absence of skin pigment and vision problems

epistasis

one gene effects phenotypic expression of another gene. Ex. two genes in Labradors: 1 for color 1 for pigment

polygenic inheritance

many genes affecting one phenotype. Ex. skin color, height, intelligence

sex-linked disorders

colorblindness, Duchene muscular dystrophy, hemophilia,

Bar body

inactive X chromosome; regulate gene dosage in females during embryotic developments allowing for male and females to express the same “dose” of x-linked genes

linked genes

located on the same chromosome and are inherited together during cell division. (if results do not follow Mendal’s Law of Independent Assortment, then the genes are probably linked.)

recombination frequency

#of recombinants / # of total offspring x 100

test cross

crossing with homozygous recessive

nondisjunction

chromosomes fail to separate properly in Meiosis 1 or Meiosis 2

aneuploidy

incorrect number of chromosomes

• monosomy ( 1 copy)

• trisomy (3 copies)

polyploidy

extra complete sets of chromosomes; 3n or 4n

• rare in animals, frequent in plants