Lecture 5 - Human Genetics Part 1

Question 1

What is a phenotype and what influences the presentation of a particular phenotype?

Answer 1

The phenotype is the observable expression of the genotype which is influenced by the environment.
E.g eye colour, hair colour.

Question 2

How many chromosomes do somatic (body) cells contain?

Answer 2

Somatic cells contain 46 chromosomes (23 pairs of chromosomes - 23 from each parent).

Question 3

What makes two chromosomes a pair?

Answer 3

Chromosome pairs are matched in size and function of their genes.

Question 4

What are autosomes? How are they numbered in a karyotype?

Answer 4

Non-sex chromosomes. They are numbered 1-22.

Question 5

What is a karyotype?

Answer 5

Description of the chromosomal content of a cell.

Question 6

How are sex chromosomes labelled in a karyotype?

Answer 6

X and Y

Question 7

What are chromosomes and when is the only time they are visible in the cell?

Answer 7

Chromosomes are made up of tightly packed chromatin. Chromatin is a comprised of DNA, RNA, histones and non-histones.

The tightly packed chromatin structures known as chromosomes are only visible during cell division, such as meiosis or mitosis. The rest of the time the chromatin is unwound like spaghetti in the nucleus of the cell.

Question 8

What is a nucleotide and what nucleotides are present in DNA and RNA?

Answer 8

A nucleotide is a nitrogen-containing base, a phosphate, and a sugar.
The nitrogen-containing bases in DNA are adenine, guanine, thymine, and cytosine. Whereas RNA has uracil instead of thymine.
The sugar in DNA is deoxyribose and the sugar in RNA is ribose.
Nucleotides in both DNA and RNA contain phosphate groups.

Question 9

What is complimentary base pairing and how does this determine the structure of DNA and RNA?
What bases are complimentary pairs.

Answer 9

The complimentary base pairs for DNA are Adenine - Thymine and Cytosine - Guanine.
And for RNA the complimentary base pairs are Adenine - Uracil and Cytosine - Guarine.

Question 10

What is a locus?

Answer 10

The physical site of a gene or DNA segment on a strand of DNA.

Question 11

What are genes?

Answer 11

Genes are sequences of DNA that encode for specific sequences of amino acids that form certain proteins.
Each gene has one or more potential effects on the phenotype of the organism.

Question 12

How does a sequence of DNA/gene influence the phenotype of an organism?

Hint: Transcription, Translation, and cell function.

Answer 12

Genes are a sequence of DNA that encode for a specific sequence of amino acids that make up a protein. Proteins affect/influence the function of a cell and cell function influences our body’s function and look.

Question 13

What is transcription?

Answer 13

Transcription is the “reading” of DNA my mRNA. Sequences of 3 mRNA base pairs code for different amino acids (known as codons).

Question 14

What is translation?

Answer 14

The “reading” of mRNA to build amino acid sequences and in turn proteins.

Question 15

What is the end product of gene expression?

Answer 15

The end product of gene expression are proteins.

Question 16

What are alleles and what percentage of human genes have two or more alleles?

Answer 16

Alleles are variations of a gene. Around 1/3 of human genes have two or more alleles.
These alleles are either dominant or recessive.

Question 17

What does it mean if an allele is dominant or recessive in regards to expression and phenotype?

Answer 17

If an allele is dominant then it will be transcribed and translated and affect the phenotype of an organism. If an allele is recessive and is paired with a dominant allele it will not be expressed. If there are two recessive alleles then they will be expressed.
If there are two dominant alleles, co-dominance, then they will both be expressed and the phentype will be influenced by both.

Question 18

What is mutation and why is it important, but can also be dangerous?

Answer 18

Mutation occurs when the sequence of DNA within a gene is altered. Mutation is what generates genetic variation and is the basis of natural selection.
It can, however, cause impairment, sometimes fatally, to the function of the organism.

Question 19

What are 4 types of mutations?

Answer 19

1. Base substitutions.
2. Deletions of DNA.
3. Insertions of DNA.
4. Whole or partial chromosomal abnormalities/changes.

Question 20

Where does the DNA in mitochondria come from?

Answer 20

The DNA in mitochondria comes from the ovum.

Question 21

In regards to genes what does homozygous and heterozygous mean?

Hint: alleles

Answer 21

If you have two of the same alleles for a gene then you are homozygous for that gene.
If you have two different alleles for that gene then you are heterozygous for that gene.