Chapter 1 - Mendel's Principles of Heredity

Genes

basic units of biological information. segments of DNA on a chromosome with discrete location

specifies protein or RNA molecules

genes specify what?

Heredity

transmission of traits from parents to offspring

Genome

total of all genes/genetic information with predictable patterns.

controls diverse array of heritable traits

the genome controls what?

Genetics

Science of heredity

structures and mechanisms of inheritance

genetics seeks to explain…

Monogenic

meaning “single gene”

Heritable traits

specific characteristics of individuals that run in families

1. sickle cell anemia

2. cystic fibrosis

examples of monogenic traits [2]

Coat colour in foxces

example of trait with two or few genes

genetic laws make testable predictions about patterns of trait inheritance

purpose of mendels laws

observable traits are determined by units of inheritance

Mendel’s hypothesis:

Artificial selection

purposeful control of mating by choice of parents for next generation

1. inherited features of offspring contributed mainly from one parent (homunculus inside sperm)

2. Parental traits mixed and permanently changed in offspring (blended inheritance)

Two key misconceptions about inheritance

1. Pea plants as experimental organism

2. traits with clear-cut alternative forms

3. created and crossed true breeding lines of pea plants with alternate forms of traits

4. reciprocal crosses

5. quantitative

6. brilliant and practical

Mendel’s experimental approach: [6]

1. Bisexual flowers (male and female parts) so they can self-fertilize

2. can be cross fertilized experimentally

3. Short breeding time

4. large numbers of progeny

why were pea plants used as experimental organisms for mendel?

antagonistic pairs

Alternate forms of a trait

1. seed colour

2. seed shape

3. flower colour

4. pod color (unripe)

5. pod shape (ripe)

6. stem length

7. flower position

Mendel had 7 antagonistic pairs that were easy to measure, with no intermediate form [7]

Hybrids

offspring of genetically dissimilar parents

Dominant

form of a trait observed in a hybrid

Reciprocal cross.

Cross with reversed characteristics of male and female parents. Controls which parents transmits a form of the trait, both parents contribute equally.

Reciprocal cross (both parents contribute equally)

The results of this disapproves the idea of a homunculus

Monohybrid cross

Mating between two true-breeding parents that differ in form of a single trait

First filial generation (F1)

Progeny of parent generation

dominant form of the trait

F1 hybrid progeny of monohybrid cross all show this phenotype:

3:1 in favour of dominant

F2 progeny of monohybrid cross show this ratio:

Reappearance of green pea colour in F2 generation

This outcome disproves blended inheritance

Gene

each individual carries two copies of this for each trait

alleles

each gene has these alternate forms:

Combination of alleles

this determines the form of a trait

Two alleles, one recessive and one dominant

In a monohybrid cross, each gene has how many alleles?

Monohybrids

individuals with two different alleles of the same gene

two of the same allele

true breeding individuals carry which alleles?

Two different alleles

F1 hybrids carry which alleles?

The two alleles of a gene separate during gamete formation, then unite at random, one from each parent, at fertilization

the law of segregation states that:

to predict the chance of a particular fertilization event

The product rule is used when?

To predict the proportion of progeny with an allele combination / form of trait

The sum rule is used when?

Product rule

The probability of two independent events occuring together is the product of their individual probabilities

Sum rule

the probability of either of two mutually exclusive events occuring is the sum of their individual probabilities

phenotype

observable form of trait

Genotype

pairs of alleles underlying the phenotype

Testcross

cross oh individual with recessive phenotype and individual with unknown dominant genotype

Dihybrid

organism that is heterozygous for two genes

Cross of true-breeding parents with alternate forms of two traits

Dihybrid cross crosses what?

Parental type

phenotype seen in parent of dihybrid cross

Recombinant type

phenotype combination not seen in parent of dihybrid cross

1:1:1:1

Ratio of possible gametes in each dihybrid parent

16

how many equally likely fertilization outcomes are there in dihybrid cross?

9

how many genotypes in the F2 progeny of dihybrid cross

4 (2 parental, 2 recombinant)

how many phenotypes in F2 progeny of dihybrid cross?

9:3:3:1

phenotypic ratio for dihybrid cross

Mate unknown genotype to individual homozygous recessive for both traits.

test cross for dihybrid:

Dominant

Which is rarer: disease caused by dominant or recessive allele?

1. long generation time

2. small families

3. little controlled mating

Why are humans not amenable to traditional genetic crosses? [3]

Pedigree

orderly diagram of family’s relevant genetic features that includes both sets of grandparents of the affected person

indicates a rare dominant trait or common recessive trait

Vertical pattern of inheritance indicates:

It produces a functional protein

why is huntingtons dominant?

parents/grandparents of individual are typically not affected but siblings may be

describe horizontal pattern of inheritance

If the trait is rare, parents are heterozygous carriers of recessive allele

horizontal pattern of inheritance indicates what?

Consanguineous mating (related individuals are more likely to both be carriers)

increases risk in horizontal inheritance

The CFTR protein regulates the passage of chloride ions. Homozygotes for the disease allele either have no CFTR protein or an abnormal protein that do not at all function or function less well.

Why is Cystic Fibrosis recessive allele?