Genetics Flashcards Preview

Year 2 - Semester 2 > Genetics > Flashcards

Flashcards in Genetics Deck (107)
Loading flashcards...

Describe penetrance

Penetrant – show signs of disorder

Non-penetrant - don’t show signs of disorder – “skips” generation


describe expressivity

variation in clinical presentation/phenotype between patients


describe x-linked inheritance

• More than one generation affected
• No male to male transmission
• Usually only males affected
• Types
o Duchenne muscular dystrophy
o Fragile x syndrome

• Carrier females can be affected due to x-inactivation which is a random process


describe autosomal dominant

• Involvement of more than one generation
• Male to male transmission
• Males and females affected equally


describe autosomal recessive

• One or more affected children with unaffected parents
• Usually only one generation affected
• Males and females affected with equal frequency and severity
• A higher incidence of consanguinity


what is the hardy weinburg equation

p 2 +2pq + q 2 = 1
Where p = normal allele and q = disease allele

q2 is the disease incidence


what is packing ratio

length of native DNA strand / length after condensation


what packing ratio do nucleosomes have

around 6


what is the 30nm fibre

coiling of beads in a helical structure
This structure increases the packing ratio to about 40.


what is the packing ratio in interphase chromosomes

about 1000


what is the most condensed state of human chromosomes

in the mitotic phase of cell division (after the chromosomes are replicated and the copies held together as sister chromatids) where they have a packing ratio of 7000-10,000 at which point – with the use of appropriate fluorescent or cytochemical stains - they can be observed by standard light microscopy.


what is the role of condensin I

lateral compaction of chromosomes in metaphase


what is the role of condensin II

axial shortening of chromosomes in prophase


what is cohesin involved with

metaphase chromosomes separating


what does the pulling of kinetochores cause

Kinetochore exerts a pulling force and when this reaches a certain force, a signal causes cohesin molecules to separate leading to neat pulling to the poles


what is trisomy 21

down syndrome


what is trisomy 18

edward syndrome


what is trisomy 13

patau syndrome


how do you name a karyotype

• Number of total chromosomes
• Then sex e.g. XX or XY
• And the a +21 for down syndrome for example


what is Klinefelter syndrome

boys with an extra X chromosome – XXY


what is turner syndrome

45 chromosomes – only 1 X in girls


what can XYY cause

impulse control problems


what can XXX cause

mild cognitive impairment


what is the difference between male and female meiosis

Male meiosis creates 4 sperm but female only produces one egg


what happens in meiosis

Homologous chromosomes join together
Homologous recombination occurs to make double stranded breaks to swap material
First meiotic division is the separation into homologous chromosomes and second divides these


what is the difference between MI and MII non-disjunction

MI non-disjunction leads to no separation of the pairs of homologous chromosomes leading to cells with 48 chromosomes and then these split to make 2 gametes with 24 chromosomes and 2 with 22 which are incompatible with life

MII non-disjunction leads to two gametes with 23, one with 24 and one with 22


what is reciprocal translocation

Non-homologous end-joining between chromosomes – where two non-homologous chromosomes are close to each other in normal homologous repair and the ends of the chromosomes are swapped

This doesn’t cause health problems but affect reproductive health – reduced sperm count in males
Also cause major malformation in the children of parents with reciprocal translocations

Genes can be interrupted by reciprocal translocation which are usually de novo and leaves them with only one functioning copy of the gene


Non-allelic homologous recombination

• Most of the human genome is unique
• There are some unusual parts where there are two identical copies in a homologue
• If these line up wrong during homologous recombination it can lead to deletions and duplications


what are acrocentric chromosomes and which are they

where the centromere is very near to one end of the chromosome

13, 14, 15, 21, 22

Others are metacentric


what are the ends of acrocentric chromosomes useful for

important for making ribosomes

All these genes to make ribosome parts are somewhat redundant which can be shown naturally by Robertsonian translocations.

This is where the short arms of two acrocentric chromosomes fuse which means that the cell only has 45 chromosomes. Again these are balanced but can lead to some infertility