Inheritance Flashcards
How many chromosomes does the average human body cell contain?
46
Or 23 pairs
How many chromosomes does the average human gamete contain?
23
Mitosis
Splitting of human body cells into 2 genetically identical daughter cells
Why does mitosis occur?
For growth, repair and development of tissue
Meiosis
Splitting of gametes to make 4 genetically different daughter cells
Where does meiosis take place
Reproductive organs
Testes/ovaries
Chromosome
Long threads that contain the molecule DNA
How are chromosomes in a diploid cell?
Each normal human body cell has 23 chromosomes
And also a copy of that cell
1 copy from the mother
And another from the father
So 46 in total
How are chromosomes in a haploid cell?
Only 23 chromosomes with no copies from parents
As they are a mix of parents dna to form your own
Because haploid cells = gametes
What is the structure of DNA called?
Double helix
Gene
Small section of DNA in a chromosome
How do genes work?
They have amino acids
That encode for a specific sequence to make a specific protein that determines an inherited characteristic
Stages of meiosis
Diploid cell in reproductive organs
Replicates copies of chromosomes
The DNA sections get swapped = variation
Divide once
Divide again = 4 different gametes
What happens in fertilisation
The sperm and egg with 23 chromosomes each combine
So makes a diploid cell with 23 pairs or 46 in total
So a pair has one chromosome from the mother and the other from the father
What happens after fertilisation?
Fertilised cell divides by MITOSIS
and creates a clump of identical cells = embryo
The cells then differentiate into different types of cells eg muscle and nerve cells
What are the contents of the double helix?
2 strands which are polymers
Joined together by small molecules
And wrapped around each other
Chromosome pairs
1 from the mother and the other for the father
Contain 2 copies of every gene therefore codes for the same characteristic
Genome
Entire genetic material of an organism
Benefits of studying human genome
Can search for genes linked to inherited diseases
Understand and treat hereditary diseases
Trace human migration patterns from the past / discover ancestry
What are the molecules DNA is a polymer of?
Nucleotides
What are nucleotides made of?
Phosphate group (circle)
Sugar molecule (pentagon)
Base (rectangle)
What changes and stays the same in nucleotides?
Phosphate (circle) and sugar ALWAYS STAY THE SAME
however the base molecule has 4 different types
4 different types of base molecules
A, C, G, T
What are the different nucleotides DNA contains?
Phosphate + sugar + A
Phosphate + sugar + C
Phosphate + sugar + G
Phosphate + sugar + T
How do strands of DNA look in terms of nucleotides?
Phosphates on the outside
Then sugars
And the base facing inside
This is mirrored for the 2nd strand
There are many rows of these
How are the bases paired?
They are complementary meaning the same bases pair on opposite strands
A with T
C with G
What is base C linked to?
Base G
What is base G linked to?
Base C
What is base A linked to?
Base T
What is base T linked to?
Base A
What are proteins made of?
Long chains of amino acids
Polymers
What determines a proteins function?
The amino acids order determines the proteins shape
And the shape of the protein determines its function
Such as being an enzyme or hormone
What determines the amino acids?
Rate the rizzness
Bases that are read in triplets determine a specific amino acid
How do bases code for specific amino acids?
The cell reads the DNA sequence of the bases in triplets
Eg ATG GGA CGC ATA
Each of these triplets encodes for a specific amino acid in the protein
Stage 1of protein synthesis
Transcription
Where does stage 1 of protein synthesis (transcription) take place?
In the nucleus
Events of transcription
Base sequence of the gene is copied into a ‘template’ molecule called mRNA
Which is single strand molecule
mRNA passes out of the nucleus
Stage 2 of protein synthesis name
Translation
Where does stage 2 of protein synthesis (translation) take place?
Cytoplasm
Events of translation
mRNA now in the cytoplasm
It attaches to a ribosome
Amino acids are bought to the ribosome on carrier molecules called tRNA
The ribosome reads the triplets of bases
And carries the correct amino acids into correct order
Thus creating the right protein chain for its right shape and function ie enzyme
What is the point of protein synthesis?
Creating the right protein by changing the order of amino acids for its specific purpose
Mutation
Caused by a change in base sequence so it encodes different amino acids which makes a different shape and different protein
Happens all the time
Do a change in amino acid sequence always cause a new protein/ mutation?
NO because different base triplets can encode for the same amino acid
Ie ACG AND TTC could code for the same amino acid
Therefore there is no effect on function of protein
What happens if a mutation does have an effect?
A different amino acid would have been coded for
And so the protein like an enzyme changes shape
So potentially it’s active site changes
What else do chromosomes contain?
Non coding parts of DNA
That can control and stop genes from producing proteins
Why do mutations occur?
If the non coding region of chromosome has a gene turned on when it should be off
It will produce a protein that shouldn’t be there
This could have a bad effect on a cell like uncontrolled mitosis = cancer
Alleles
Different versions of genes that code for different characteristics
Genotype
Tells us the alleles present
Ie XX or XY
Homozygous
2 copies of the same allele
Like XX
Homo = same
Phenotype
The characteristic as a result of the genotype
Heterozygous
2 different alleles
Like XY
Herero = different
Dominant allele
It will show in the phenotype even if there’s only one copy
Like XY
The Y is dominant here
This therefore will give decide someone’s phenotype even if it’s heterozygous
Recessive allele
Only shows in phenotype if there are 2 copies present
Like XX
The x is usually recessive because if it’s XY it will be a male but because there’s 2 it will be a female
What is Cystic fibrosis ?
Disorder of cell membranes
How is cystic fibrosis inherited?
Allele for normal cell function is dominant = C
Allele for cystic fibrosis is recessive = c
Therefore you have to have 2 copies of this aka cc to inherit it
Carrier
Someone who carries the dominant allele for a characteristic
Polydactyly
Disorder with extra fingers or toes
How is polydactyly inherited?
A dominant allele
So only having one of them will express the disorder, despite having the allele for normal one
Is it possible to be a carrier of polydactyly?
No because it’s caused by a dominant allele so just having 1 = expressed
How to prevent inherited disorders?
Embryo screening to look for them
Potentially = gene therapy by correcting alleles
Embryo screening
Checking to see if they have alleles present for disorder
And implanting ones without it into mother
Issues with embryo expensive
Too expensive
Many embryos destroyed which is seen as unethical
Slippery slope that it may result in screening for specific characteristics
What determines the sex of an offspring?
The 23rd pair of chromosomes
One from mother XX and one from father XY
