Inheritance Flashcards
What are the rules for monohybrid crosses?
Upper case = dominant Lower case = recessive Label parents + their phenotype Label parental gametes (circle them) Draw punnet square Always write dominate allele first State phenotypes Ratio
What is a monohybrid cross?
A cross in which alleles of only one gene are involved
What is monohybrid inheritance?
Inheritance of single genes
What are monohybrid crosses used to do?
To determine dominant relationship between two alleles
What will be the phenotype of offspring with parents with Rr?
R = orange skin
r = blue skin
3:1 RR Rr Rr rr
What are diploid organisms characteristics determined by?
Alleles in pairs
What is pure-breeding?
When both homologous organisms are bred
What does pure-breeding result in?
1st filial (F1) generation
How many alleles can be present in a single gene?
Only one of each pair
Can pure-breeding varieties be crossed with other pure-breeding varieties?
YES
What is dihybrid inheritance?
Inheritance of 2 characteristics at the same time
What does dihybrid crosses/inheritance show?
Shows how 2 characteristics, determined by 2 different genes, located on different chromosomes are inherited
What did Mendel discover about peas?
Round + yellow = dominant
Wrinkled + green = recessive
What phenotypes would be produced if you crossed yellow + round peas?
Genotype = RrYy
9:3:3:1 Yellow + round Round + green Yellow + wrinkled Wrinkled + green
Why does F2 in dihybrid inheritance have 4 types of gametes?
As gene for colour + gene for shape are on separate chromosomes
What does it mean their is random assortment in meiosis?
There can be either shape allele
+ either colour allele
What does it mean that fertilisation is random?
Dihybrid inheritance
So any 4 gametes with one parent can mix with any 4 gametes from another parent
How many gametes should dihybrid have?
4
What is the Law of Independent Assortment?
Each member of a pair of alleles may combine randomly with either of another pair
What is codominance?
When both alleles are expressed in the phenotype; neither are dominant or recessive - they are equally dominant
What are the rules to consider with codominance crosses?
Can’t use upper + lower case
Use different letters in stead
Subscript = gene in question
What is an example of codominant?
CR CR
CW CW
CR CW
What is the genotype for a red flower in codominance?
CR CR
What is the genotype for a white flower in codominance?
CW CW
What is the genotype for a pink flower in codominance?
CR CW
Why is a pink flower produced when there it is heterozygous codominant?
As single functioning allele only produces enough pigment for pink
What phenotype would be produced if you crosses a codominant white and red flower?
Pink flowers 1:1:1:1
What phenotype would be produced if you crossed the codominant F1 generation?
Pink flowers
1:2:1 C*R C*R C*W C*W C*R C*W C*R C*W
What are multiple alleles?
When alleles have more than 2 alternative forms of a single gene, located at the same loci of homologous chromosomes
What is an example of a polygenetic phenotype?
Eye colour
What is polygenetic determined by?
Several genes at different loci
What are the three human blood group alleles associated with?
Immunoglobulin gene (I)
What are the three human blood group alleles?
IA
IB
I*o
What does gene I dictate?
The presence of certain antigens on the cell surface of a RBC
What antigen does I*A present?
A
Round-shaped
What antigen does I*B present?
B
Pointy triangular-shape
What antigen does I*o present?
Neither
No antigen present on RBC
Even though there is 3 blood group alleles how many are present in one individual?
2
Why are only 2 blood group ales only present in one individual?
As only 2 homologous chromosomes, so only 2 gene loci
What are IA + IB?
Codominant
What is I*o?
Recessive
How many possible blood groups is there?
4
What are the four different blood groups
A
B
AB
O
What are the possible genotypes of blood group A?
IA IA
IA Io
What are the possible genotypes of blood group B?
IB IB
IB Io
What are the possible genotypes of blood group AB?
IA IB
What are the possible genotypes of blood group O?
Io Io
Why can I*o be present in blood group A + B?
Because I*o is recessive so doesn’t change phenotype
What antigens will blood group AB have present?
Rounded + pointy triangular
What antigens will blood group A have present?
Rounded
What antigens will blood group B have present?
Point-triangular
What antigens will blood group O have present?
NONE
What phenotype is produced when you cross
IA IB
Io Io
2:2 I*A I*o I*B I*o Blood group A + B Offspring don't have same blood group as parents
What phenotypes would be produced if you crossed F1 blood group generations?
IA Io
IB Io
1:1:1:1
What should you get if you cross heterozygous blood groups?
1:1:1:1
What is one chromosome composed of before replication?
One DNA molecule
What is one chromosome composed of after replication?
Two identical DNA molecules
What does it mean about the chromosome after replication?
Amount of DNA increases but no. of chromosomes stay the same
How many chromosomes is there?
46
How many pairs of chromosomes is there?
23
How many out of the 23 are homologous pairs?
22
Why is the 23rd pair no homologous?
Because it is the sex cells
X and Y
What are genes located on X or Y?
Sex-linked
What is the difference between the structure of X and Y?
X is longer than Y
What does it mean that X is longer than Y?
Genes found on X do not have a homologous equivalent on Y
What are males?
XY
What are females?
XX
Why are recessive characteristics more common in males?
As no homologous section on Y that could carry dominant allele
What is haemophilia?
Blood doesn’t clot correctly
So leads to excessive bleeding following a cut or internal bleeding
Fatal is not treated
What sex cell is haemophilia linked to?
X
What type of genetic disorder is it?
Recessive
What does the haemophilia genes code for?
Alternative base sequence = faulty protein
What can the healthy protein to treat haemophilia be produced by?
GM organisms
What phenotype would be produced if a carrier female was crossed with a normal male?
1:1:1:1
When doing a sex linage cross what must you include?
The X and Y
So you can see which gender has what alleles
When doing sec linkage cross what must you always say as well as the phenotypes?
Genders
What is a carrier?
Someone who has the genotype to pass on the genetic disorder but it is not expressed in their phenotype
What does it mean if any 2 genes are found on the same chromosome?
They are linked
What is formed when all genes are on a single chromosome?
Linkage group
What is autosomal linkage?
When 2 or more genes are carried on the same autosome
What happens to all linked genes in meiosis?
They all stay together
What does it mean that all linked genes stay together during meiosis?
They will pass on into gametes together
So will pass into offspring together
Does autosomal linkage follow Mendel’s Law of Independent Assortment?
NO
Why doesn’t autosomal linkage follow Mendel’s Law of Independent Assortment?
Since each allele is not free to mix with either allele from another pair
Which cross produces the ratio 3:1?
Monohybrid - 2 heterozygous
Which cross produces the ratio 9:3:3:1?
Dihybrid - 2 heterozygous
Which cross produces the ratio 1:1:1:1?
Blood group - heterozygous A + B
Sex linkage - carrier female, normal male
Which cross produces the ratio 1:2:1?
Codominance - heterozygous
What is epistasis?
When the allele of one gene affects/masks the expression of another in the phenotype
Describe agouti
Wild type
Grey/brown
Banded
AABB, AaBB, AABb, AaBb
Describe albino
No melanin
Hs to have bb
AAbb, Aabb, aabb
Describe black
Uniform black hairs
No banding
aaBb, aaBB
What phenotypes are produced when two agouti (AaBb) mice are crossed?
9:4:3
Agouti: White : Black
Why is an albino mouse produced when bb is present?
Because if there is no melanin = gene A cannot be expressed
What is produced if a dominant allele is present in a biochemical pathway?
Functional enzyme
What is produced if homozygous recessive is present in a biochemical pathway?
Non-functional enzyme
Disrupt pathway
What is a biochemical pathway?
Some genes act in a sequence by coding for specific enzymes in pathway
Explain how a mutation could cause an enzyme not to work
Mutation causes change in sequence (write where it changes)
= change in sequence of amino acids
= changes tertiary structure of protein
= active site no longer complementary
Explain how it shows the man is heterozygous
Inherited recessive from mother
Normal allele from father
Father doesn’t have recessive allele or would have it
Explain why Mendel’s work was not accepted
Wasn’t much scientific evidence about genetics yet
Already had pre-considered conditions
Why might the prediction of fur type not be proved right?
Fertilisation is random
Describe the difference between dominant + recessive alleles
Recessive not expressed in the presence of dominant alleles
Describe the difference between alleles and genes
Gene is a section of DNA that codes for a specific sequence of amino acids
Allele is a version of a gene
Describe the difference between homozygous + heterozygous chromosomes
Homozygous = same alleles Heterozygous = contain different alleles
Explain how meiosis results in plants producing gametes with certain genotypes
Homologous pairs halved
Independent assortment
What is a recessive allele?
An allele that mist be homozygous to produce a trait and won’t be expressed in the presence of a dominant allele
What is a dominant allele?
The one that is always expressed
Why would farmers only want calves of the same sex?
Females for milk
How does the diagram show it is a recessive allele?
Unaffected parents have unaffected offspring
Give examples from diagram!
Explain why observed ratios are often not the same as expected ratios
Fertilisation random
OR not large enough sample size
Use gene linkage to explain results
All linked genes stay together during meiosis
GgNn individuals produce mainly GN + gn gametes
Gn + gN come from crossing over so fewer of them
USE EXAMPLES IN QUESTION
What environmental factors affect egg production?
Temperature
Light intensity
Explain why genes being close together on chromosome when identifying potential phenotype of offspring
Reduces chance of crossing over
If crossed over = mixture of gametes
Explain how the genotype bbee produces yellow coat colour
All homozygous recessive = no enzyme produce
Stays yellow
Explain how the genotype BbEe produces black coat
Two dominant = both enzymes produced
Two conversions take place
Explain how to get white, red and purple flowers in this biochemical pathway
Both genes are involved in producing the different colours as one gene controls the expression of another - epistasis
White flower = Gene 1 + 2 both must have homozygous recessive alleles = neither enzyme produced = remain white
Red flower = Gene 1 must have at least one dominant allele so the 1st enzyme can be produced = convert pigment red. BUT gene 2 must have homozygous recessive alleles = enzyme 2 isn’t produced = no conversion from red to purple
Purple flower = Gene 1 + 2 must both have at least 1 dominant allele so both enzymes can be produced= 2 conversions of colour
What is the loci?
Specific physical location of a gene on a chromosome
What is a histone?
Protein that provides structural support to a chromosome
What is a chromatid?
One of 2 identical halves of a replicated chromosome
What is a chromosome?
A long, coiled molecule of DNA that carriers genetic information in the form of genes
