Inheritance

Question 1

What is meant by F1 and F2 generation?
In terms of true breeding speciemens what would the genotype be

Answer 1

Parent : homozygous
F1 is the first set of offspring - heterozygous
F2 is the second set of offspring - can’t predict

Question 2

What is meant by true breading?

Answer 2

Produce genetically identical offspring, able to self-pollinate.
Are homozygous

Question 3

What is mendelian inheritance?

Answer 3

The pattern of inheritance from parents to offspring of one gene with TWO alleles as the only options.

Question 4

What are the three laws of mendelian inheritance?

Answer 4

Law of segregation
Law of independent assortment
Principle of dominance

Question 5

What is the law of segregation?

Answer 5

An individual has two alleles for one gene
Only one allele, selected randomly is passed onto the offspring.

Question 6

What is the law of independent assortment?

Answer 6

That genes at different loci seperate into gamates randomly
E.g inheriting alle 1 of gene 1 does not make you more likley to inherit allele 1 of gene 2
Each chromosome is inherited randomly and independently of other chromosomes

Question 7

What is the principle of dominance?

Answer 7

That one allele masks the experession of another.

Question 8

What is meant by autosomal dominant?
What are some example of diseases?

Answer 8

One mutated copy of a gene found on a non-sex chromosome, is sufficient to cause expression of a disease.
Huntington disease, Marfan syndrome

Question 9

What factors affect the level of dominance?
What are the different types of dominance?

Answer 9

Dominance is relative to the function of the protein and the nature of the mutation (allele)
A condition may be
dominant - masks the other
incomplete dominance - partial effect over the other allele
Co-dominance - both alleles are expressed in the phenotype.

Question 10

What is the difference between co-dominance and incomplete dominance?

Answer 10

Co-dominant - two phenotypes are expressed simultaneously
Incomplete dominance - results in a thrid phenotype

Question 11

What is an autosome?

Answer 11

A chromosome that is not a sex chromosome, not pair chromsone 23

Question 12

What is the pattern of huntingtons disease inheritance?

Answer 12

Mutation for repeat CAG sequence, more repeats is a more degenerative disease,
Less repeats causes a disease that appears later in life (often after passed to children)
Is a rare fatal neurological disease
Dominant and autosomal

Question 13

What is an example of a sporadic autosomal dominant condition?

Answer 13

Retinoblastoma mutation

Question 14

What is meant by an autosomal recessive condition?

Answer 14

A mutation on chromosome 1-22, requires two mutated alleles in order for it to be expressed.
Typically skip generations.
Has carriers.

Question 15

What are some examples of autosomal recessive conditions?

Answer 15

Cystic fibrosis
Sickle Cell Disease

Question 16

What is the pattern of inheritance and genetic trends in sickle cell disease?

Answer 16

Autosomal recessive pattern
Most commonly in African descent
Heterozygous characters may express a partial phenotype with some symptoms, also provides a genetic advantage more likley to have less severe malaria.

Question 17

What is meant by X-linked Dominant condition?

Answer 17

Loci on the x-chromosome, only one copy needed to be expressed.

Question 18

What is an example of an x-linked dominant condition?

Answer 18

Fragile X syndrome
Males experience more severe syndromes as only one copy of the allele
Fragile X causes more copies of the CGG repeats
Not life threatening, delays neurological development

Question 19

What is a x-linked recessive condition?

Answer 19

Mutation on a x chromosome, that can be masked by a wild type allele on the corresponding gene on a second chromosome if present.
Females require two copies of the mutated allele to express the condition.
More commonly expressed in the phenotype of men compared for women.

Question 20

What are some examples of the x-linked recessive conditions?

Answer 20

Haemophilia
Fabry disease.

Question 21

What is the pattern of inheritance of Fabry disease?

Answer 21

An inherited disorder that is x-linked recessive conditions.
Affects mainly the heart and kidneys.
Often have problems with breaking down globotriaosylceramine (GL-3).
Is a lysosomal storage disorder.

Question 22

What is the deal with Y linked disorders?

Answer 22

XY males are always affected.
Not many known
ONly around 200 genes on the y chromosome
Only passed from father to son, not in females
Are often sporadic as frequently cause infertility by affecting the AZF region responsible for sperm production.

Question 23

What type of inheritance it blood group an example of?

Answer 23

Non-mendelian, co-dominance as in there are three potential alleles and of the two alleles that the patient poses both are expressed in the phenotype.

Question 24

Give an overview of the inheritance of different blood groups.

Answer 24

There are three major alleles A, B and O
This creates four phenotypes blood group A, B, AB and O.
O is recessvie to all other blood groups and A/B are co-dominant.

Question 25

What is the deal with mitochondrial DNA inheritance?

Answer 25

DNA is located in the mitochondria
Passed from mother to children exclusivly, hence will have an identical mitochondrial DNA to anyone in the same maternal lineage.
However, mitochondrial DNA mutates at a more frequent rate due to lack of protective histones.

Question 26

What is meant by heritability?

Answer 26

A statistical concept (h2) that measures how well differences in peoples genes account for differences in their traits.
The estimate is specific to one population in one environment, and can change over time as circumstances change.
Note it explains the likilihood of variation being due to genetics or environment, not what causes the trait.

Question 27

Explain the meaning of different heritability estimates.

Answer 27

Estimate ranges from zero to one.
Zero indicates that almost all of the variablility is due to environment (religion, language spoken etc) whilst one indicates almost all is due to genetics.

Question 28

How does mutation causing disease link to heretibality?

Answer 28

Polygenic - higher influence from the environment, these are often more complex traits such as intelligence or personality
Monogenic - changes due to one gene, very little impact from the environment.

Question 29

Why do some disorders not follow the patterns of mendelian inheritance?

Answer 29

Are polygenic
Caused by interactions of the genes with the environment.
This includes type 2 diabetes, heart disease, cancers etc.
Or disorders are due to the changes in the number of structure of chromosomes.

Question 30

What is meant by a multifactoral condition?

Answer 30

When a trait results from several factors inlcuding interactions between genes and environmental factors.
This is the most common cause of human traits.

Question 31

What is the key idea of epigenetics?

Answer 31

It is dynamic and reversible
Modification to DNA or histones
DNA methylation - decrease expression
HIstone Acetylation - increase expression.

Question 32

What is human karyotype?

Answer 32

A labratory produced image of a persons complete set of chromosomes in numbered order from one cell.
Chromosomes are stained by giemsa.
Used to look for abnormalities in chromosome structure or function.

Question 33

What is meant by a diploid cell?

Answer 33

Contains two copies of each chromosome, as shown in human somatic cells.
2n = 46

Question 34

What is meant by homologous chromosomes?

Answer 34

Two chromosomes in a pair, contain the same genes but different alleles.
Often one from mam and one from dad.

Question 35

What is a haploid cell?

Answer 35

Known as n
Contains one set of chromosomes
These are human gamete cells
n = 26

Question 36

Describe the process of mitosis.

Answer 36

Interphase: cellular components are replicated
G1 - cell duplicates specific molecules and structres and grows
S - Cell replicates DNA
G2 - cell duplicates structures and grows
Interphase chromosomes are uncondensed
Prophase: chromosomes condense, spindle appartus appears, nuclear envelope breaks down
Metaphase ; Middle
Anaphase: Chromatids pulled to opposite poles of the cell.
Telophase : spindle dissociates and nuclear envelope reforms
Cytokinesis: Cell membrane divides
Results in two genetically identical daughter cells (2n).

Question 37

What are the stages of meiosis?

Answer 37

MEIOSIS 1
Prophase: synapsis and crossing over occur, chromosomes condense and becomes visible, nuclear envelope fragments, spindle fibres attach to chromosomes
Metaphase: Homologous chromosomes arrange in pairs down the equator of the cell.
Anaphase: Homologous chromosomes are pulled to opposite poles of the cell
Telophase: Nuclear envelop partially reforms, spindle apparatus disapears and cytokinesis occurs, Resulting in two n cells.
MEIOSIS 2
Prophase: Nucleus envelope fragments, spindle apparatus forms
Metaphase: Chromosomes arranges down the equator of the cell
Anaphase: Sister chromatids are pulled to opposite poles of the cell
Telophase: Nuclear envelop reforms around two daughter nculei, chromosomes decondense, spindle appartus disappears.
Resutls in four genetically different gamete cells (haploid - n).

Question 38

What is meant by synapsis and crossing over in meiosis?

Answer 38

Synopsis is the pairing of homologous chromosomes
Occurs during prophase 1 when chromosomes arrange in homologous pairs (this is synapsis)
Crossing over occurs when a chiasms forms, and alleles (of the same gene) are exchanged between homologous chromosomes.

Question 39

What two mechanism results in genetic variation resulting from meiosis?

Answer 39

Independent assortment - each daughter cell recieves one chromosome from each homologous pair, the combination of maternal and paternal chromosomes are divided randomly,
Crossing over - creates new combinations of alleles (s very rare)

Question 40

Explain the genetic trends of chromosomal disorders?

Answer 40

It is possible to inherti some chromosomal disorders but most are spontaneous.

Question 41

What are the different types of chromosomal mutations?

Answer 41

Polyploidy - changes in the numbr of whole sets of chromosomes, often have three of four complete sets opposed to two
Non-disjunction - increase in the copies of one particular chromosome, due to failure of homologous chromosomes to seperate during meiosis 1.

Question 42

Give an example of a chromosomal disorder.

Answer 42

Tuner Syndrome
Instead of a 46XX genotype, the female is missing an X chromosome so has a 45XO genotye, This is a non-dysjunction mutation
It can be mosaic, where not all cells have lost the chromosome.
Common symptoms include: constriction of aorta, poor breast and repoructive system development, small fingernails, short stature, brown spots, shiled shaped thorax and distinct facial features including a webbed neck.

Question 43

What is gametogenesis?

Answer 43

The production of gamete cells from haploid precursor cells, aka the process of meiosis.