B1 More Genetic Diagrams Flashcards
What are gametes in sexual reproduction?
Reproductive cells from the mother and father (egg and sperm)
What is contained in a each gamete?
One copy of each chromosome, so gametes only have one version of each gene, one allele.
How are offspring produced? (We’re thinking about the gametes)
The chromosomes from a male gamete get mixed up with those from a female gamete.
What does the offspring end up with?
Pairs of chromosomes and two alleles for each gene.
What does it mean if the alleles are different?
The organism has instruction for two different versions of a characteristic but it only shows now version.
What is the version of the characteristics displayed decided by?
The dominant allele
What is the name for the allele that is not displayed when an organism has different alleles?
Recessive allele
If a characteristic is caused by a recessive allele, when is it displayed?
When both alleles are recessive.
How are dominant alleles shown in genetic diagram?
As a capital letter
How are recessive alleles shown in a genetic diagram?
With a small letter
What does it mean if you are homozygous for a trait?
You have alleles the same for that particular gene.
What does it mean if you are heterozygous for a trait?
You have two different alleles
What is it called if you have two alleles the same?
Homozygous
What is it called if you have two alleles that are different?
Heterozygous
What is a genotype?
The alleles an organism has.
What is a phenotype?
The characteristics an organism displays.
What is single gene inheritance?
A characteristics controlled by a single gene, e.g. Blood group
What can genetic diagrams help predict?
The phenotype of the offspring, when you know the genotype of the parents.
Look at genetic diagrams and practice drawing them
P7 in the revision guide.
The height of garden pea plants is controlled by a single gen with two alleles. The allele for tall plants (T) is dominant over the allele for dwarf plants (t). Two heterozygous pea plants are crossed. Draw a genetic diagram to find what proportion of the offspring would be expected to be dwarf plants (3 marks)
I in 4, need to see a diagram
How many chromosomes are there in every human body cell?
23 pairs
How are the 23rd pair of chromosomes in the human body cell labelled?
XY or XX
What do the sex chromosomes decide?
Whether you are male or female
What type of chromosomes are XX or XY?
Sex chromosomes
What are male sex chromosomes labelled?
XY
What are female sex chromosomes labelled?
XX
How is sex determined?
By genes
What does Y chromosome carry?
A gene which makes an embryo develop into a male as it grows, by stimulating growth of the testes
Draw a genetic diagram for sex inheritance
XX. (Female parent)
X. X.
X. XX. XX.
(Male parent) XY
Y. XY. XY
What do a sex inheritance genetic diagram show?
Two XX genotypes, two XY genotypes
There is a 50% chance of having a boy or girl
Ratio 50:50 boys to girls
What is CF (cystic fibrosis)?
A genetic disorder of the cell membrane
What is CF (cystic fibrosis) caused by?
A recessive allele, which is carried by about 1 in 30 people
People with only one copy of the recessive gene for cystic fibrosis are called what?
Carriers
How does having one copy of the recessive gene affect a person?
Because the allele is recessive they won’t have the disorder, they are known as carriers.
If a child has a chance of inheriting the disorder cystic fibrosis, what must be true?
Both parents either have the disorder themselves or are carriers.
Draw a family tree genetic diagram to show the likelihood of a child having cystic fibrosis if both parents are carriers.
Ff carrier
FF unaffected
ff has CF
1in 4 chance see p8 for diagram (25%)
1 in 2 chance of being a carrier (50%)
