Genetics Flashcards
Define inheritance
Passing of hereditary traits from one generation to the next
What is the difference between genotype and phenotype?
Genotype The genetic makeup of an organism Can be determined by observing DNA Completely depends on gene sequences Inherited by offspring
Phenotype
Visual properties and behaviours of the organism
Determined by observing outward characteristics
Depends on genotype and environmental factors
Not inherited by offspring
What are homologous chromosomes?
Homologous chromosomes are the chromosomes which contain alleles for the same type of genes (both look the same)
What are non-homologous chromosomes?
Non-Homologous chromosomes are chromosomes that contain alleles for different type of genes
What is an allele?
A different form of the same gene
BB dominant
bb recessive
What is homozygous?
A person with the same alleles on both chromosomes
What is heterozygous?
Having different alleles on homologous chromosomes
Heterozygous individuals are carriers of a recessive gene
What type of genotype leads to PKU?
Homozygous recessive
What is the term for fraternal twins and how are they formed?
Dizygotic
The independent release of 2 oocytes (cells in the ovary) fertilized by 2 separate sperm
What is the term for identical twins and how are they formed?
Monozygotic
2 individuals that develop from a single fertilized ovum
genetically identical & always the same sex
If ovum does not completely separate, conjoined twins (share body structures)
Name the 4 types of bases that make up a strand of DNA
Tymine (T)
Adenine (A)
Guanine (G)
Cytosine (C)
How many chromosomes do human body cells contain?
46 chromosomes
23 pairs
What are chromosomes made of?
DNA
What is the term/name of chromosomes 1-22?
Autosomes
What is the 23rd pair of chromosomes called?
Sex chromosomes
XX = Female XY = Male
What is a karyotype?
A pattern of either a male or female chromosomes
46, XY = Male
46, XX = Female
What chromosomes is the gene for cystic fibrosis located?
Chromosome 7
What chromosomes is the gene for sickle cell disease located?
Chromosome 11
What type of order are genes arranged in on a chromosome?
Linear
Define nondisjunction
Chromosomes fail to separate properly
Cell with one or more extra or missing chromosomes is called an aneuploid
(2n-1) is missing a chromosome
(2n+1) has an extra chromosome
Define aneuploid
Cell with one or more extra or missing chromosomes
Define translocation
Location of chromosome segment is moved
Crossing-over between 2 nonhomologous chromosomes
Down syndrome results from a portion of chromosome 21 becoming part of another chromosome
Individuals have 3 copies of that part of chromosome 21
3 most common autosome anomalies
Down syndrome (trisomy 21: 47,XX,+21)
Edwards syndrome (trisomy 18: 47,XX,+18)
Patau syndrome (trisomy 13: 47,XX+13)
2 most common sex chromosome anomalies
Turner syndrome 45,X
Klinefelter syndrome 47,XXY
What causes down syndrome?
Nondisjunction of chromosome 21 (trisomy 21)
More common in older mothers due to more exposure to radiation & chromosome-damaging chemicals
1 in 800 infants is born with Down syndrome
mental retardation, distinctive facial structures & malformation of the heart, ears, hands & feet
Define mutation
An alteration or change in the genetic material
Causes of a mutation
Inherited
Exposure to mutagenic agents
Spontaneously through errors in DNA replication/repair
What is amniocentesis? Describe the process? At how many weeks?
Pre-natal diagnosis to detect chromosome abnormalities
Take 10-20 ml amniotic fluid at 15-17 weeks gestation
A syringe inserted through the abdomen under ultrasound guidance
Foetal cells cultured for chromosome analysis
Risk of miscarriage about 0.5%; small risk of infection
If termination- labour is induced
Why would someone get a prenatal diagnosis?
Avoid birth of affected baby eg with Down Syndrome
Know in advance & prepare for birth/treatment
Relieve uncertainty
Define genes
Genes are codes for cells to make proteins
Genes are located on chromosomes
The term for alterations in single genes
Single gene disorder
The term for variants in genes
Multifactorial disease (+environment)
Chromosomal imbalance term
Chromosome disorder
What are the 3 types of single gene disorders?
Autosomal dominant - always expresses itself
Autosomal recessive - only expresses in the absence of dominant unaltered gene – healthy carrier
X-linked - genes found on X chromosomes
Define autosomal dominant, recissive and x-linked recissive
Dominant
These individuals are called Heterozygotes with one copy of the altered gene they are affected
Recessive
Homozygotes must have two copies of the altered gene to be affected
X-linked recessive
Males with an altered gene on the X-chromosome are always affected
Name 3 audtosomal dominant conditions
Huntington disease
Neurofibromatosis type 1
Marfan syndrome
Familial hypercholesterolemia
Familial Adenomatous Polyposis (FAP)
Prader-willi
Name 3 autosomal recissive conditions
Sickle Cell disease
Cystic fibrosis
Batten Disease
Congenital deafness
Phenylketonuria (PKU)
Spinal muscular atrophy
Recessive blindness
Maple syrup urine disease
Signs of Marfan syndrome
Tall stature
Elongated thin limbs and fingers
High risk of heart defects
Disloacted lens
Signs of sickle disease
Abnormal haemoglobin
Bony infarcations in the phalanges and metacarpals can result in unequal finger length
Name 3 x-linked recissive conditions
Fragile X syndrome
Haemophilia
Duchenne muscular dystrophy (DMD) (Becker BMD)
Fabry disease
Retinitis pigmentosa
Alport syndrome
Hunter syndrome
Ocular albinism
Adrenoleucodystrophy
Signs of Fragile x syndrome
Causes mental retardation in some of males with this gene
learning disabilities, oversized ears, enlarged testes & double jointedness
may be involved with autism
Unaffected males may pass gene onto daughters whose children may suffer
Name 4 common polygenic disorders
Alzheimer’s
Diabetes
Cancer
Eczema
Define multifactorial inheritance
Inheritance controlled by many genes plus the effects of the environment
The term for environmental influences that cause development defects
Teratogens
Name 3 teratogens and what they affect
Chemicals & Drugs
Fetal alcohol syndrome = slow growth, facial features, defective heart & CNS
Cocaine = attention problems, hyperirritability, seizures
Cigarette Smoking
Low birth weight, cleft lip & palate, SIDS
Irradiation or radioisotopes during the first trimester
Mental retardation, microcephaly
