Genetics & Family History

Question 1

Describe structure and function of DNA in cell

Answer 1

Found in nucleus of cell, carries our genetic material.
Made up of Deoxyribose sugar, nucleotide and phosphate.
The four nucleotides cytosine and thymine (pyramiding) and adenine and guanine (purine), G-C have three hydrogen bonds between and A-T have two hydrogen bonds. Nucleotides are linked via phosphate to form backbone (forms phosphodiester bonds) . The two strands of DNA run the opposite way from each other to allow nucleotides to match up.

Question 2

Explain process of DNA replication

Answer 2

Enzyme gyrase unzips DNA enzyme helical unwinds DNA, by breaking hydrogen bonds between base pairs.
Enzyme primate start process of rebuilding separate strands, makes a small piece of RNA (tells strand to rebuild).
DNA polymerase adds bases in 5’ to 3’ end direction making strand in small chunks,. Forms hydrogen bonds between primers and of strand.

Question 3

Describe the structure and function of RNA

Answer 3

RNA present in all organisms is single stranded has a ribose sugar, alternating phosphate and nucleotides (uracil instead of thymine). Some RNA involved in regulating gene expression found in cells nucleus, cytoplasm and organelles.

Question 4

What are chromosomes and describe the different types

Answer 4

Chromosomes are bundles of DNA, wrapped tightly around a histone (a protein which gives structure to long strand of DA.
There are 46 chromosomes, 23 pairs. 22 of the pairs are Autosomes meaning not sex linked and also has varying amount of genes chromosome 1 may have 2800 genes where’s 22 has 750 genes. The 23rd chromosome is sex detaining so XX or XY.

Question 5

What is a Diploid cell

Answer 5

All cells in human body are diploid except for sperm and egg cell. They contain all genetic material and contain 46 chromosomes. Divide by mitosis producing identical versions of themselves.

Question 6

What are the stages of mitosis?

Answer 6

1. Interphase: most of cells life in this phase DNA replicates.
2. Prophase: DNA condenses becoming more visible and membrane around nucleus disappears.
3. Metaphase: chromosomes line up in middle of cell
4. Anaphase: chromosomes are pulled to diff ends of cell
5. Telophase: new membrane forms around chromosome at each end of cell
6. Cytokinesis: cell membrane pinches and divides into two daughter cells.

Question 7

Describe features of haploid cell (what is it)

Answer 7

In humans they’re only sperm and egg cells, contain only half of our genetic material only 23 chromosomes.
Made by diploid cell via meiosis which forms four genetically different daughter cells. This provides variation in offspring.

Question 8

Stages of meiosis

Answer 8

Interphase, prophase (crossing over), metaphase, anaphase, telophase, cytokinesis
Prophase II (crossing over), Metaphase II (independent assortment), Anaphase II, Telophase II, Cytokinesis II.

Question 9

Define gene and allele

Answer 9

Gene: a section of DNA that codes for a particular protein
Allele: different versions of the same gene (variation)

Question 10

Single - gene disorder
What is Autosomal Dominant?

Answer 10

This is when the dominant gene in the abnormal gene eg Huntington’s disease, if one parent is affected there’s 50% chance offspring will be. There can be no carriers of this gene as it is dominant.

Question 11

What is Autosomal Recessive?

Answer 11

The abnormal gene is recessive and therefore requires two copies (both parents must have the gene) to cause disorder) eg sickle cell, cystic fibrosis. There can be carriers of this gene as it is recessive if both parents are carriers there’s a 25% chance offspring will be affected.

Question 12

Sex linked
What is X linked recessive

Answer 12

This is when the condition is recessive and only on the X chromosome, women are more likely to be carriers as they have two X chromosomes whereas men are more likely to be affected as they only have one chromosome. Eg Haemophili A

Question 13

What is X linked dominant?

Answer 13

This is when the abnormal gene is dominant and will always be expressed eg Fragile X, no carriers.

Question 14

What are other more complex types of inheritance

Answer 14

Co-dominance: some genes share dominance and effect eg AB blood
Multiple allele: more than two forms
Polygenic: multiple genes responsible for one trait
Multifactorial: involve interaction of gene and environment

Question 15

Explain blood group inheritance

Answer 15

A: is dominant could be IAIA or IAi
B: dominant IBIB or IBi
AB: Co-dominant so IAIB
O: recessive so ii