GENETICS
1. Gregor Mendel is known as the Father of Genetics. Based on experiments with
garden peas, he concluded that traits are passed from parents to offspring
through heredity. These inherited traits control physical & behavioral
characteristics of an organism will look & how it will behave.
2. Genes are segments of DNA on chromosomes. Many genes are located together
on the same chromosome.
3. Individual genes called alleles are received from each parent & act together to
produce inherited traits in offspring.
4. Genetic variation among members of a species is created by:
a) alleles are randomly distributed on chromosomes
b) during meiosis a process called crossing over may cause alleles to
exchange places on a chromosome
5. These terms genetically describe an organism:
a) genotype - genetic makeup of an organism - when both alleles in pair are
alike, the organism is homozygous/pure - if the 2 alleles pair are
different, the organism is heterozygous/hybrid/carrier
b) phenotype - appearance of organism resulting from expression of
genotype
6. Mendel’s work showed these patterns of inheritance for different traits:
a) dominance & recessiveness - dominant allele (cataracts, polydactyly,
dwarfism) covers effect of recessive allele (albinism, cystic fibrosis) a recessive trait appears only 2 recessive alleles are paired together
b) incomplete dominance - both alleles influence trait & produce a new
blended trait (red + white = pink snapdragons)
c) codominance - both alleles are expressed equally (red + white = roan
horses & black + white = checkered chickens)
d) multiple alleles - 3 or more alleles of same gene act together (ABO
blood type, pigeon feather color, & coat color in rabbits)
e) polygenic - 2 or more gene pairs act together (skin, hair, & eye color
& height)
f) sex-linked - found only on X or Y sex chromosome - X-linked traits
primarily affect males (X - colorblindness, muscular dystrophy, &
hemophilia; Y - hairy ears)
g) gene expression can be influenced by environment: hormones (baldness &
peacock feathers), temperature, nutrition, light, & chemicals (leaf size &
shape)
7. Biologists use a diagram called a Punnett square to predict the probability of
certain traits being inherited by offspring. A cross between individuals
involving 1 pair of contrasting traits is a monohybrid cross.
8. A testcross can determine whether an organism with a dominant phenotype is
homozygous or heterozygous. By crossing the individual of unknown genotype
with a homozygous recessive individual, the offspring will provide the answer.
9. Humans have 23 pairs of homologous chromosomes. 22 pairs are called
autosomes & the 23rd pair is different in males & females & determines the
sex of an individual & are called sex chromosomes (X & Y).
a) Female gametes (eggs) each receive an X chromosome.
b) Male gametes (sperm) receive either an X or Y chromosome.
c) Eggs fertilized by sperm carrying the X chromosome produce XX/female.
d) Egg fertilized by sperm carrying the Y chromosome produce XY/male.
10. Genetic screening examines & analyzes genetic makeup:
a) amniocentesis - removal of small amount of amniotic fluid for analysis
b) chorionic villi sampling - removing a small piece of tissue from between
uterus & placenta for analysis
c) karyotype - chromosomes from cells in the amniotic fluid or chorionic
tissue are photographed for analysis
d) pedigree - family tree record showing inheritance patterns over several
generations can be analyzed to determine carriers of a trait (P1, F1, F2)