Chromosomes, cell division, inheritance and genetic disorders. Flashcards
what are Nucleolus?
A dense, non membrane bound mass in the nucleus. It contains proteins and nucleic acids and DNA.
What is DNA?
‘Deoxyribonucleic acid’
It is a double helix chain of nucleotides with complement pairs Cytosine/Guanine and Adenine/Thymine. Wrapped around proteins and gets
condensed into chromosomes before and during cell division.
What are chromosomes?
DNA packaged into chromosomes that are only visible at cell division.
How many chromosomes per person and its breakdown?
46 chromosomes or 23 pairs.
Two copies of each type of chromosome
Homologous pairs of Mum and dad
1 pair of sex chromosomes
X and Y
Females XX or males XY (X from mum, Y from dad)
X chromosomes larger and carry more genes
22 pairs of autosomes which are all the other chromosomes.
Why do cells divide?
Cell populations need to be maintained. Can be killed or stressed by environmental conditions. They can live from several hours to decades for example Skin cells live for 2 3 weeks and RBCs can live ~120 days. Cells can also self destruct (undergo apoptosis) when damaged or compromised.
What are the 2 types of cell division and what do they need to undergo these processes and the purpose?
Mitosis: Process of cell division somatic cells creates 2 identical daughter cells 46 chromosomes needed Purpose is growth, repair and to replace
Meiosis:
Occurs in ovaries and testes to produce ova and
sperm.
Gametes
produces 4 different daughter cells
23 chromosomes needed
purpose is reproduction.
Mitosis step by step (5)
- Interphase: DNA replication
- Pro phase: Nuclear membrane disappears. Chromosomes condense and become visible under
microscope. Preparation of chromosomes for mitosis by lining up on the metaphase plate. - Metaphase: Spindle fibres form chromosomes meet in the middle.
- Anaphase: Sister chromosomes pulled apart.
- Telophase: Nuclear membrane reforms around new group of chromosomes. Cell pinches apart and two identical diploid daughter cells are formed. The separation into two.
Meiosis step by step
It is exactly like mitosis but the process is done twice. resulting in 4 cells with 2 half chromosomes for reproduction where the other half is with the female.
What is apoptosis
Programmed cell death. Normal part of cell cycle where the cell self destructs. E.g. webbing between fingers of embryo. It reduces harmful DNA mutations. Failure of apoptosis may lead to cancer.
what is genetic code
The blueprint for all proteins made in the body. Sequence of DNA that codes for one protein.
What is the sequence from amino acids to organisms?
Amino acids proteins tissue cells tissue organs organism
Transcription
Make a copy of the DNA (mRNA version) it is completed in the nucleus.
Translation
Read the DNA instructions from the
mRNA copy and put together an amino acid chain
based on the sequence (protein synthesis) and it is completed in the cytoplasm.
What are genotypes and phenotypes?
Genotype: the genetic composition of an individual.
Phenotype: the observable traits of an individual.
Determined by genotype, influenced by the environment for example identical twins studies.
What are alleles?
Alleles are different variants of a gene for example functional insulin and non functional insulin and A antigen or B antigen on RBC. Genes can have many different alleles such as A, B or o allele for RBC antigens.
What is homozygous or heterozygous?
Homozygous: 2 alleles/copies the same (XX or xx)
Heterozygous: 2 different alleles/copies (Xx)
Heterozygous individuals have 2 different sets of
instruction in which to follow which depends on the dominance of the trait.
Dominant and recessive genes
Dominant/recessive: one allele is always expressed
(dominant), and the other is not. Recessive allele can only be expressed if no dominant allele is present (i.e., homozygous recessive) or in rare cases codominance occurs where both alleles are expressed (cc + xx = cx)
what are mutations?
Change in DNA sequence however it does not always change the protein produced. Mutations can be either deleterious or beneficial.
Deleterious and beneficial mutations
Deleterious = bad for the individual Beneficial = advantage for the individual
Autosomal recessive disorders
Phenotype is expressed in the homozygote only. Frequency and severity of disorder is the same for males and females. Example: Phenylketonuria PP = normal (no disease) Pp = normal carrier pp = individual has disorder
Autosomal dominant disorders
Dominant allele is the undesired condition. Frequency and severity of disorder is the same in males and females. Example: Huntington’s Most affected people are heterozygotes hh = normal (no disease) Hh = affected (has Huntington's)
Sex linked inheritance
Sex linked inheritance = male female rates differ, males more often affected. Being color blind is X linked Genotypes Female: X C X C , X C X c , X c X c Male: X C Y, X c Y Phenotypes Wildtype: X C X C , X C X c , X C Y Colour blind: X c X c , X c Y
Mutations on the DNA level (base mutation)
Occurs during the time of DNA replication and can be as simple as on of the nucleotides going in the wrong spot in the sequence.
What is a environmental factor of mutations at the DNA level?
Cancer
Mutations at the chromosome level.
Much more serious than base mutations. Entire genes/chromosomes involved in duplication, deletion, inversion and translocation.
An example is Trisomy 21 (Down’s syndrome) Klinefelter Syndrome (XXY)/Turner syndrome (45 XO). Cri du chat (5p minus) (piece of chromosome 5 is missing)
