B1 You And Your Genes Flashcards
Where do you find the instructions for how an organism develops?
In the nucleus of a cell
What is a gene?
A small section of the DNA that makes up chromosomes in the nuclei of cells
Explain the function of a gene?
They instruct the cell how to make proteins
Proteins can be structural e.g. Keratin in hair or enzymes e.g. Amylase
Which cells have only a copy of one chromosome from each pair?
Sex cells (sperm and egg cells)
What is another word for sex cells
Gametes
What sex chromosomes do males have?
XY
What sex chromosomes to females have?
XX
What chromosome pair do you find the instructions for sex-determination
Hint: this is where the cell knows if you are going to be XX (girl) or XY (boy)
Chromosome pair 23
How many chromosomes does a diploid cell have?
Hint: diploid just means a full set of chromosomes….
23 pairs which is 46 chromosomes in total
How many chromosomes do haploid cells have?
Hint: haploid means a half set of chromosomes, one from each pair
23 chromosomes
Where do the pairs of chromosomes come from?
One chromosome from mothers egg cell and one chromosome from fathers sperm cell
What are alleles?
Different versions of a gene.
Example: we may inherit the short nose gene from our father and the long nose gene from our mother- if the short nose gene is DOMINANT then we will have a short nose
What does homozygous mean?
That a person carries two copies of the same allele for any gene
What does heterozygous mean?
A person carries two different alleles for any gene
Why do offspring (children) look similar to their parents?
They have a combination of alleles from their mothers and fathers when an egg cell is fertilised by a sperm cell
Give an example of a characteristic in humans that is determined by several genes working together?
Eye colour or blood group
How many alleles are there usually on each gene?
Two
One from egg cell (mum) the other from sperm cell (dad)
Explain why you don’t look the same as your brother or sister when you have the same parents?
Each person inherits a different combination of maternal and paternal genes during fertilisation and therefore shows different characteristics
What is genotype?
The combination of alleles for a gene usually written as letters
E.g. Tt, tt or TT are all genotypes, they show us what alleles are present
If a genotype is Tt and the gene it is coding for is being tall, what does the T mean?
The capital letter T means the allele is dominant- if a person has this allele it doesn’t matter what the other allele is because T is dominant and therefore the person will be tall
If the alleles for foot length are F for big feet and f for small feet.
Mum is Ff and dad is Ff what combination of alleles might their child have and what is the % chance of them having a child with small feet?
Mum has F and f
Dad has F and f
Combinations FF, Ff, fF, ff
75% chance of big feet 25% of small feet as you would need to have two recessive alleles ff to have small feet. The presence of F in any genotype would mean you have big feet as it is the dominant allele
