3.4 + 10.2 Inheritance

Question 1

Mendel’s discoveries and conclusions

Answer 1

Discoveries:

• when purebreads were crossed only one characteristic appeared
• when Mendel self-fertilised the offspring - characteristics resulted in 3:1 ratio

Conclusions:

• organisms have discrete factors that determine features
• organisms posses two versions of each factor
• gamete contains only one version of each factor
• parents contribute equally to characteristics of offspring
• for each factor one version is dominant against another, so it will be complete;y expressed

Question 2

Mendelian rules

Answer 2

1. Law of segregation: when gametes form, alleles are separated, so each gamete carries only one allele
2. Law of independent assortment: segregation of alleles for one characteristic occurs independently from other alleles (not true for genes on the same chrom. - linked genes)
3. Principle of dominance: recessive alleles will be masked by dominant (not all genes show dominant hierarchy - co-dominance, incomplete dominance)

Question 3

Why do gametes acrry only one allele?

Answer 3

Because gametes are haploid - one chromosome - only one allele present

Question 4

What is the male genotype of sex chromosomes?

Answer 4

Hemizygous - males have only one allele on sex chromosomes

Question 5

Types of zygosity

Answer 5

• homozygous
• heterozygous
• hemizygous

Question 6

Define genotype

Answer 6

GENOTYPE: gene composition for a specific trait

Characteristics are determined by both genotype and environment

Question 7

Define co-dominance

Answer 7

CO-DOMINANCE: when both alleles are expressed equally in the phenotype of a heterozygous organism - altered phenotype

Question 8

example of co-dominance

Answer 8

BLOOD GROUPS: human RBC can be categorised into different groups based on glycoproteins (antigen) on tehir surface

Isoantigens:

A, B - codominant

O - recessive

Question 9

Monohybrid cross

Answer 9

Question 10

Genotypes of genetic disease

Answer 10

• autosomal recessive (both alleles needed)
• autosomal dominant (one or two alleles)
• co-dominant (one allele needed) but heterozygous milder symptoms than homozygous

Question 11

Explain cystic fibrosis

Answer 11

• autosomal recessive, mutation in CFTR gene on chromosome 7
• individual produces mucus which clogs airways and secretory ducts in digestion system -> rwspiratory failure and pancreatic cysts

Question 12

Explain Huntington’s disease

Answer 12

• autosomal dominant, mutation in Huntingtin gene on chrom. 4 - around 40 CAG repeats causes Huntingtin protein misfold - neurodegeneration
• usually in late adultohood

Question 13

What are sex linked genes?

Answer 13

SEX LINKED GENES: genes which are located on sex chrom.

Sex linked conditions usually on X chrom, as Y chrom very short - not many genes present

X linked recessive traits more common in men - only one X chrom (no balance of dom) - only females can be carriers

Question 14

Examples of X linked recessive conditions

Answer 14

• red-green colour blindness: mutation of red green photoreceptors on X chrom.
• haemophilia: body’s ability to control blood clotting is impaired - coagulation factor genes on X chrom

Question 15

Define mutagens and their types

Answer 15

Mutagens - agents which increase the rate of mutations

1. UV
2. Radiation
3. Biological (bacteria, viruses)

Question 16

What is a pedigree chart?

Answer 16

PEDIGREE CHART: chart representing genetic history of a family over several generations

Males - squares

Females - circles

Horizontal line - mating

Oldest on the left

Question 17

Dihybrid cross Punett grid

Answer 17

Ratios 9:3:3:1 if two heterozygotic for both phenotypes crossed

Question 19

Unlinked genes vs linked genes Punett grid

Answer 19

Question 20

Example of linked gene in Drosophilla

Answer 20

Question 21

How can an offspring have a different allele than the parents?

Answer 21

An offspring has a recombinant gene - after corssing over i meiosis 1 of non-sister chromatids

Question 22

Recombinant allele frequency is population compared to non-recombinant

Answer 22

Recombinant alleles are less common - corssing over is random - the further are two genes on homologous chromatids - the more likely is that recombination - more place for chiasmata to form

Question 23

Phenotype differences in linked vs unlinked genes (AaBb x aabb)

Answer 23

Question 24

Explain chi suqared test

Answer 24

Chi squared - statistical measure that determines whether difference between observed and expected frequency distribution

Steps:

• create hypotheses (null vs alternative)
• construct a table with observed vs expected frequencies
• apply chi formula:
• determine the degree of freedom (df): df = (rows-1) (columns-1)
• identify p value (p<0.05 - difference unsignificant - results reliable)

Question 25

Monogenic vs polygenic inheritance

Answer 25

MONOGENIC: (phenotype controlled by single loci) - exhibit discrete variation in phenotypes (sex)

POLYGENIC: (phenotype controlled by several loci) - exhibit continuous variation in phenotypes (height, skin colour, eye colour)

Increase in number of gene loci that contribute to phenotype - more different exhibited - _Gaussian (bell-shaped) distributio_n

Charactertics not only detemrined by genetics but also by environment - skin colour