lecture 13: mendelian genetics

Question 1

What did Mendel study? (2)

Answer 1

Heredity and how are traits passed on from parents to offspring?
—> Gave basics of genetics and explain a big part of them

Question 2

What are the 2 hypotheses for heredity?

Answer 2

1. Blending hypothesis

2. Particulate hypothesis

Question 3

What is the blending hypothesis?

Answer 3

Idea that genetic material from the two parents blends together to produce a trait

Question 4

What is the particulate hypothesis?

Answer 4

Idea that parents pass genetic material as discrete heritable units (now known as “alleles”) that interact to produce a trait —>correct hypothesis

Question 5

What are the 5 aspects of Mendel’s study?

Answer 5

1. Used pea plants as model organism
2. Many varieties of these plants with distinct traits for various heritable characters
3. Matings are controlled: take sperm and egg from white/purple or contrary
4. Matings produce many offsprings
5. Track many characters in either-or manner (two traits)

Question 6

Mendel’s Experiment Design?

Answer 6

1. Parental generation (P): true-breeding (of 1 trait) X true-breeding (of trait 2) —> purple flower X white flower
2. 1st first filial generation offspring (F1)
3. Self-pollination (self-fertilization) of F1
4. 2nd filial generation offspring (F2)

Question 7

What is true-breeding?

Answer 7

Plants that produce offspring of the same variety when they self-fertilize

Question 8

What are Mendel’s three principles of inheritance?

Answer 8

1. Segregation
2. Dominance
3. Independent Assortment

Question 9

What happened at the F1 generation? (hybrids)

Answer 9

All hybrid plants of F1 were purple

Question 10

What happened at F2 generation?

Answer 10

3:1 ratio of purple to white flowers

Question 11

Mendel conclusion?

Answer 11

• Observed same pattern of inheritance in six other pea plant characters (3:1 ratio)
• Results support particulate hypothesis of heredity

Question 12

What is Mendel’s model? (5)

Answer 12

1. For each character, an organism inherits one heritable factor (gene) from each parent
2. Alternative versions (alleles) of these heritable factors account for variations in inherited characters
3. One allele is dominant while the other is recessive
4. The heritable factors (genes). are segregated (separated) during gamete formation and are packaged into different gametes
5. Sex of parent passing on the allele does not affect the inheritance pattern —> give same results

Question 13

What is a Punnett square?

Answer 13

Matrix which predicts the probability of an offspring’s genotype and phenotype for a particular set of parents

Question 14

What are the phenotypic ratios and genotypic ratios in Mendel’s study?

Answer 14

Genotypic Ratio: 3:1 purple vs white

Phenotypic Ratio: 1 homozygous dominant (PP), 2 heterozygous (Pp), 1 homozygous recessive (pp)

Question 15

What makes an allele dominant and what makes it recessive?

Answer 15

Dominant: when effects of an allele can detected regardless of the alternative allele
Recessive: if the effect of an allele is masked in the heterozygous condition

Question 16

How can mendelian traits in humans be disorders?

Answer 16

• Disorders caused by one gene (monogenic disorders)

- Can be inherited as a recessive or dominant trait depending on the allele involved in the disorder

Question 17

What are carriers?

Answer 17

Heterozygotes that have a disorder inherited in a recessive fashion

Question 18

What is albinism?

Answer 18

• Problem with pigmentation of skin and hair

- A recessive disorder (aa) —> homozygous recessive

Question 19

What is achondroplasia (dwarfism)?

Answer 19

• Dominant disorder (Dd; heterozygous or homozygous dominant)
• Only possibility to be “normal” = dd = homozygous recessive) —> so impossible to be a carrier and have dwarfism —> so two no-dwarf parents cannot have a dwarf child

Question 20

Does dominance have to do with frequency in population?

Answer 20

No, the dominant allele is not the most prevalent in population
- Concerns only the alleles

Question 21

What is a monohybrid cross and a dihydrid cross?

Answer 21

Hybrid following a single character

Question 22

What are the two characters that Mendel studied for his dihybrid crosses?

Answer 22

Colour (yellow and green) and shape (round and wrinkled)

Question 23

What were the dominant and recessive traits in Mendel dihybrid crosses?

Answer 23

Dominant: Yellow and Round
Recessive: Green and Wrinkled

Question 24

What are the 2 hypotheses of Mendel’s dihybrid crosses?

Answer 24

1. Dependent Assortment

2. Independent Assortment

Question 25

What is Dependent Assortment?

Answer 25

Traits are inherited as a package —> alleles are linked and assorted dependently into the same gamete —> can only have the same combinations as the parents

Question 26

What is Independent Assortment?

Answer 26

Traits are not inherited as a package —> alleles are not linked and are independently assorted into gametes —> parental combinations but also new combinations

Question 27

Which of the 2 hypotheses did Mendel observe and what was the phenotypic ratio?

Answer 27

Independent assortment

9:3:3:1

Question 28

What two informations explain Mendel’s laws of segregation and independent assortment and how?

Answer 28

1. Chromosomes are the vehicles of heredity

2. How meiosis works and shuffles alleles into unique combinations

Question 29

What two informations explain how alleles arise and how some alleles are dominant or recessive?

Answer 29

1. Genes are the units of heredity

2. What genre are, how they work, and how mutation can change them

Question 30

Explain “Chromosomes are vehicles of heredity.”

Answer 30

• All genes contribute to specific character —> found at specific locations (loci) —> on specific chromosome
• We inherit homologous chromosomes for every chromosome —> therefore pairs of each gene
• Pairs of genes can differ —> different versions (different alleles) OR can be identical (different alleles) —> encode different proteins —> lead to different traits

—>SEGREGATION: packages ONLY 1 of the homologous pairs in gametes

Question 31

Explain the principle of segregation

Answer 31

Alleles segregate during gametogenesis because they are located on homologous chromosomes (1 on each) and these chromosomes are separated during Meiosis I

Question 32

Explain principle of independent assortment

Answer 32

Alleles are assorted independently because the genes are located on different chromosomes —> during Meiosis I, maternal and paternal chromosomes from homologous sets are RANDOMLY DISTRIBUTED into daughter cells

Question 33

Explain “genes are units of of heredity” and what are the consequences of this?

Answer 33

Different genes = Different genotype = May cause differences in phenotype —> How alleles arise

Question 34

How could an allele be dominant (normal)?

Answer 34

Dominant (normal) alleles encode a functional protein while recessive alleles produce non-functional proteins —> Need enough functional protein to produce a normal phenotype

Question 35

What is a protein P and what is its relationship with phenotype?

Answer 35

• An enzyme
• Amount of functional protein P = molecular connection between genotype and phenotype —> having functional protein P = having normal phenotype

Question 36

What is complete dominance?

Answer 36

Where dominant allele completely masks the effect of the recessive allele in heterozygous conditions —> normal (dominant) phenotype

Question 37

Is having one copy of the normal (dominant) allele enough to produce a normal phenotype?

Answer 37

Yes. One copy produces enough functional proteins = produce normal phenotype

Question 38

Does Mendel’s Model explain all characters?

Answer 38

No, the inheritance pattern of MOST characters do not follow his simple model

Question 39

What are the 2 components of the Theory of Inheritance?

Answer 39

1. Principle of Segregation

2. Principle of Independent Assortment