genetics SB1 vocab

Genes

basic units of biological info

• passed down from one generation to the next, underlie formation of every heritable trait

• DNA region that specifies a particular protein/RNA

heredity

the way genes transmit traits from parents to offspring

4 Mendelian Themes

1. variation in traits = widespread in nature

2. variation = essential for following genes from one generation to the next

3. variation = inherited according to patterns

4. heredity apply equally well to all sxually reproducing organisms

artificial selection

selective breeding of domesitcated plants and animals w desirable characteristics

• issues:

  • one parent contributes most to an offspring’s inherited features

  • blended inheritance

What did Mendel to differently from those who preceded him?

1. chose garden pea— has both sperm producing and egg producing organs (stamens and pistils, respctively)—> easy to self-fertilize

2. used no intermediate forms AKA discrete traits

3. collected lines of peas that bred true— pure breeding lines produce offspring that carry traits from parents that remain constant from generation to generation

   1. also used antagonistic pairs (purple x white, yellow x green) to cross fertilize and produce hybrids— hybrid progeny always had the characteristics of one parent

4. recriprocal crosses— reversed characteristics of male and female parents, controlling whether a characteristic was transmitted via sperm or egg

   1. hybrid progeny produced by reciprocal cross fertilizations had same characteristics, therefore doesn’t matter which parent was male/female

Mendel’s Monohybrid Cross

P1: homozygous yellow and green crossed (yellow dominant to green)

F1: all yellow, but heterozygous yellow

F2: heterozygous cross —> 3:1 ratio

Monohybrid Crosses

• crosses btwn parents that differ in only one trait

law of segregation

two alleles of each gene separate during gamete formation, uniting at random, one from each parent @ fertilization

Product Rule

probability of two or more indp events occurring together is the product of the probablities that each event will occur by itself

• probability of event 1 and event 2 = probability of event 1 x probability of event 2

phenotype

observable characteristic

genotype

pair of alleles present in an individual

testcross

(1) a cross used to determine the genotype of an individual showing a dominant phenotype by mating with an individual showing the recessive phenotype; and (2) a cross used to determine whether genes are linked and the distance (recombination frequency) between linked genes

Dihybrid cross

• 9:3:3:1

  • only 9 different genotypes exist out of 16 allelic combos

• produces parental types and recombinant types

• crosses btwn individuals that are heterozygous at two different genes.

parental types

phenotypes that reflect a previously existing parental combination of alleles that is retained during gamete formation

recombinant types

phenotypes reflecting a new combination of alleles that occurred during gamete formation

Law of Indp Assortment

during gamete formation, different pairs of alleles segregate indp of each other

2 general important molecular principals

1. specific gene determines specific protein

2. dominant allele determines normally functioning protein, recessive allele doesn’t specify a functional protein

Rare Dominant Trait Pedigree

• vertical inheritance

• at least one affected person in each generation

• view mating btwn affected and unaffected partner as analogous to a testcross

• if some offspring don’t have the dominant inheritance disease, the parent showing the trait is heterozygote

• ex: huntington’s

• affected children always have at least one affected parent

• dominant traits show a vertical pattern of inheritance: the trait shows up in every generation

• two affected parents can produce unaffected children, if both parents are heterozygotes

Rare Recessive Trait Pedigree

• horizontal pattern of inheritance

  • phenotypes reflecting a new combination of alleles that occurred during gamete formation

• skips generations

• ex: cystic fibrosis

• unaffected can indicate carriers

• affected individuals can be the children of two unaffected carriers

• all children of two affected parents should be affected

• rare recessive traits —> horizontal pattern of inheritance: trait first appears in one or more members of one generation and not seen in earlier generations

• recessive traits may show a vertical pattern of inheritance if the trait is extremely common in the population