lecture 11- intro to human genetics Flashcards
down syndrome
People with Down’s syndrome have distinctive physical characteristics Sloping forehead Protruding tongue Short stubby limbs Slightly flattened nose Almond-shaped eyes May have congenital eye, ear and heart defects These are examples of a phenotype
phenotype
Observable properties of an organism produced by the genotype and environmental influences Examples include: Hair colour Exective function abilities Short/tall Lung capacity Psychiatric condition Skin tone
nucleus
Every cell in the human body, except red blood cells, has a nucleus
It contains the majority of the cell’s genetic material
It stores this material in the form of chromosomes
Chromosomes
A chromosome is a thread-like structure consisting of chromatin
It carries the genetic information of the body, arranged in a linear sequence
Chromatin is made up of nucleic acids (DNA and RNA) and proteins
Chromosomes are only visible during cell division processes, called mitosis and meiosis. Otherwise, they unfold and uncoil into a diffuse network within the nucleus
karotype
The karyotype is a description of the chromosomal content of a cell, including a total count of the chromosomes and a description of the sex chromosomes
Most of our cells contain 46 chromosomes (23 maternal and 23 paternal sets)
The gametes (sex cells; sperm from male and egg from female) each contain 23 chromosomes
The 46 chromosomes are actually 23 pairs (1 from mother, 1 from father)
Each chromosome pair carries genes of the same type
These chromosome-pairs match in size, shape, and the functions they serve
karyotype continued
Each parent contributes 23 chromosomes to each child
The autosomes (non-sex chromosomes) are numbered 1 to 22
The sex chromosomes are either X or Y
Females have two copies of the X chromosome
Males have a copy of the X and Y
The X chromosome is considerably larger than the Y and contains more genetic information
karoyotype 3
47, X Y + 21= male down syndrome
47, XX+21= female down syndrome
45, X-turners syndrome
47,XXY-klinefelters syndrome
Klinefelter’s syndrome
XXY condition can affect development in three ways
Physical development: weak muscles and reduced strength. Lagging in physical development.
Language development: Between 25 and 85% of XXY males have some language difficulties
Social development: XXY males tend to be more quiet and undemanding compared with XY males
Deoxyribonucleic acid (DNA)
Complementary base pairing
Nucleotide (base + sugar + phosphate group
Anti-parallel strands
Primary structure (sequence) of DNA is described by the order of the bases in a 5’ to 3’ direction
Humans have ~ 3.3 x 109 bases
The locus is used to describe a sequence of DNA situated on a specific region on a chromosome
DNA is a double-stranded structure consisting of 2 nucleotides held together by hydrogen bonds between the bases in opposing strands
DNA molecules are organised into stretches of sequence called genes
genes
Each gene has one or more specific effects upon the phenotype of the organism.
A gene can recombine with another gene
A gene can mutate into different forms
Genes are expressed at different time points in life
A gene can only influence development when it is turned on and is expressed
For the DNA to impart information, it must first by transcribed
Transcription and Translation
The strand of DNA acts as a template for the synthesis of ribonucleic acid (RNA)
Like DNA, RNA forms stable structures by base-pairing
DNA information can be copied to RNA for transcription and translation and carried to other areas of the cell to create proteins
Messenger RNA carries the instructions specifying sequences of amino acids
Groups of three bases of mRNA serially code for each amino acid.
These groups of 3 bases are called codons
There are potentially 64 possible codons, but in nature there are only 20 different amino acids
proteins
Proteins are the end product of gene expression
20 different amino acids
But when you think of all the combinations of 20 in a string of molecules, the potential for diversity (clearly) is staggering
protein types
Enzymes Hemoglobin Insulin Collagen Keratin Histones Actin and myosin Immunoglobulins
alleles
About one-third of human genes have two or more different forms, called alleles
An allele is one of two or more forms (or variations) of a gene
The alleles of a given gene influence the same trait or characteristic
E.g. eye colour
The different allele forms result in different eye colours (green, brown, hazel, grey etc)
gene expression
The dominant allele is the form of the gene that is expressed if present.
The recessive allele is not expressed if a dominant allele is present.
polygenic inheritance
When traits are governed by more than one gene
Applies to most traits and behaviors of interest to behavioral scientists
mitosis
Mitosis is a process of cell replication and division, in which the cell separates the chromosomes in the cell nucleus into two identical sets, in two separate nuclei
These two daughter cells are genetically identical to each other and their parent cell
each cell 46 chromosomes
meiosis
Meiosis is a special type of cell division, necessary for sexual reproduction.
Meiosis produces gametes
The DNA is replication and the cell divides twice
each cell 23 chromosomes
mutations
Mutation is the process of change in the sequence of DNA
Without mutations, all human life would begin life as a clone and only environmental influences would alter what we observe in the phenotype
Mutations are the source of genetic variation and the basis for natural selection
They are also the source of genetic damage that contributes to cell death, genetic disease and cancer
Mutations have a wide range of effects on organisms, depending on the type and location of mutation
They can occur spontaneously or be induced by external factors such as exposure to chemicals and radiation
There are four main types of mutations
Base substitutions
Deletions of DNA
Insertions of DNA
Whole or partial chromosomal abnormalities
summary
The phenotype is the observable outcome of the genotype
Recombination of genetic material enables genetic variation in the population
DNA codes for protein manufacture
Mitosis is chromosome replication and division
Meiosis is chromosome replication, recombination, division and division again
Mutations are the source of genetic variation and are the basis of natural selection
