Genetics

Question 1

What are chromosomes

Answer 1

Long molecules of DNA wrapped around proteins called histones

Question 2

What is a chromatin

Answer 2

Chromatin refers to a mixture of DNA and proteins that form the chromosomes found in the cells of humans and other higher organisms.

Question 3

What happens when there are multiple chromatins wrapped tightly with one another

Answer 3

Forms a chromosome

Question 4

How can you identify how many chromosomes there are from looking at a diagram

Answer 4

Count the number of centromeres. As such, even a centromere with one chromatid connected to it is considered one chromosome, which is the same number of chromosomes as a centromere with two chromatids attached to it

Question 5

What is a gene

Answer 5

Sections along DNA that encode for proteins. It is the gene sequence determining the amino acid sequence for the protein it encodes

Question 6

What does diploid mean

Answer 6

2 copies of each chromosome/chromatids

(this is the double chromatid thing observed)

Question 7

What does haploid mean

Answer 7

Non homologus chromosome/chromatid (just 1 chromsome/chromatid)

(this is the single chromatid thing observed)

Question 8

What does homologous mean

Answer 8

pairing at meiosis and having the same structural features and pattern of genes.

I.e. the genes are in the same places

Question 9

What are autosomes

Answer 9

These are considered chromosomes numbered from 1-22.

These don’t determine our sex. Homologous (each chromosome pair are same in size)

Question 10

What are sex chromosomes

Answer 10

This is the 23r chromosome. These determine our sex

Question 11

What is the chromosome for a male

Answer 11

XY

Question 12

What is the chromosome for a female

Answer 12

XX

Question 13

What is the trend in size of chromosomes

Answer 13

As they increase in their numbers (i.e. chromosome 1, chromosome 2, chromosome 3, etc.), it typically goes from large to smallest, with smallest at chromosome 22 and largest at chromosome 1

Question 14

When chromosomes are homologous what do we observe with the genes

Answer 14

The same gene is found on the same location (locus) on the homologous chromosomes

However, the DNA sequence for the same gene on these chromosomes may still have some variations

Question 15

What is an allele

Answer 15

Different variants/versions/forms of a gene due to their slight differences in DNA sequence.

Thus, several alleles are possible for one gene. FOr example, there are 3 possible alleles for the ABO gene

However, only 2 different alleles are present at the gene’s locus in an individual

Question 16

What is a genotype

Answer 16

Combination of alleles for a particular gene

Question 17

What does a homozygous genotype mean

Answer 17

Means the alleles are the same.

I.e. homozygous dominant, homozygous recessive

Question 18

What does a heterozygous genotype mean

Answer 18

Means the alleles are different.

Question 19

What does phenotype mean

Answer 19

The observable or measurable characteristic arising from the genotype and its interactions with the environment

I.e. these are thingss we can see with our naked eye our measurable through lenses such as hair colour

Question 20

What do dominant alleles do

Answer 20

These are able to mask the effect of recessive alleles

Typically characterised by a capital letter

Question 21

What are some important things to note about dominant alleles

Answer 21

Not about preferential expression

Not necessarily more common in a population

Not necessarily the normal allele

Question 22

What do recessive alleles do

Answer 22

They have their effect masked by dominant alleles

Typically characterised by lowercase letter

Question 23

What are some important things to note about recessive alleles

Answer 23

Encoded proteins may still retain some normal function, but at a reduced capacity or completely dysfunctional

Can be more common in some populations

Don’t necessarily give genetic diseases

Question 24

What is codominance

Answer 24

Occurs when two different alleles and therefore phenotypes are expressed equally.

I.e. AB blood type

Question 25

What causes dominant phenotypes

Answer 25

Homozygous dominant genotypes

Heterozygous genotypes

Question 26

What causes recessive phenotypes

Answer 26

Homozygous recessive genotypes only

Question 27

What chromosomes are able to determine sex

Answer 27

X and Y chromosomes which is seen in the 23rd pair

Question 28

What does hemizygous mean

Answer 28

A term that describes a person who has only one copy of a gene rather than the usual two copies. Hemizygosity can occur under normal conditions. For example, because most males have one X chromosome and one Y chromosome, they are hemizygous for genes on those chromosomes.

Question 29

What are the consequences of having hemizygous sex chromosomes for a male

Answer 29

It means that for either the x or y chromosome, any allele would affect the phenotype of the individual (whether it be recessive or dominant). This is because it doesn’t allow the opportunity for anything heterozygous, and as theres only one that one thing will determine the whole phenotype

Question 30

What are the different sex linked disorders

Answer 30

X - linked dominant

X - linked recessive

Y- linked

Question 31

Explain X - linked dominant

Answer 31

It suggests the abnormal allele is dominant and lies on an X chromosome

Lets say that the abnormal allele is dominant A, and the normal allele is recessive ‘a’

For the expression of this phenotype, affected females can have a homozygous dominant xA xA, or they could be heterozygous xA xa

For the expression of this phenotype, as males are hemizygous, there is only one expression; xA y (i.e. one abnormal allele is sufficient to cause the disease)

Question 32

Explain X - linked recessive

Answer 32

It suggests the abnormal allele is recessive and lies on the x chromosome

Lets say the abnormal allele is recessive a. and the normal allele is dominant A

Affected females have a homozygous recessive genotype xa xa

Meanwhile, for males it doesn’t matter if its recessive because they are hemizygous, this showing the genotype; xa y, which would depict the phenotype a anyways.

In this case, heterozygous females are carriers

Question 33

What does it mean by carriers

Answer 33

I.e. unaffected but carry an affected genotype (for recessive mothers)

Question 34

What is haemophilia

Answer 34

This is where there is a clotting deficiency, and abnormal alleles code for proteins that cant participate effectively in blood clotting process

Two types; haemophilia A and haemophilia B

This is an x linked recessive disorder

Question 35

What is haemophilia A

Answer 35

Most common type

Deficiency of clotting factor 8

Question 36

What is haemophilia B

Answer 36

Defciency of clotting factor 9

Question 37

Are females often carriers of haemoophillia

Answer 37

Yes, they can have a heterozygous genotype; generally have a healthy phenotype and may have some mild symptoms of haemophilia.

Severe symptoms is rare but possible despite having the heterozygous genotype

Question 38

How can hemophilia continue to manifest in females

Answer 38

The process of x chromosome inactivation (lyonisation)

Here one of the two X chromosomes in each diploid cell becomes inactivated during early development. Selection is random. This is to prevent females from having twice as many X chromosome gene products as males

On average, 50% of material X chromosome are 50% of paternal X chromosome is inactivated. However, this could be disproportionate

This could mean that there might be skewed X inactivation, where affected X with haemophilia gene is more active than the unaffected X

Question 39

Punnet squares

Answer 39

Yes