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BIOLOGY TOPIC 3 GENETICS


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BIOLOGY TOPIC 3 GENETICS


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Sammy Universe


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[Front]


what is non-disjunction? (2)
[Back]


when chromosomes don't separate properly = extra or missing chromosomes aneuploidy

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BIOLOGY TOPIC 3 GENETICS - Detalles

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Why are sickle shaped blood cells useless? (3)
Can't carry O2 properly = anemia forms clots
Why are sickle shaped blood cells useless? (3)
Can't carry O2 properly = anemia forms clots
Why are sickle shaped blood cells useless? (3)
Can't carry O2 properly = anemia forms clots
What is a gene?
DNA segment that influences heritable characteristic and occupies a specific position on a chromosome
What is an allele? how do they differ?
Different forms of genes differs by bases
Why are sickle shaped blood cells useless? (3)
Can't carry O2 properly = anemia forms clots
Why are sickle shaped blood cells useless? (3)
Can't carry O2 properly = anemia forms clots
What is a genome?
All of the genetic info of an organism
What is locus? (loci)
Specific position of a gene on a chromosome
What are the 3 things used to identify a gene?
Chromosome number arm (P= short q= long) region + band
What is the difference between alleles and genes?
Gene is a more general characteristic (eye color) allele is specific (blue eyes)
What is a mutation?
Change in nucleotide sequence = changes the function of an encoded protein
What are mutagens?
Agents that mutate genetic material
What are 3 examples of chemical mutagens?
Carcinogen processed food cleaning products
What are 2 examples of biological mutagens?
Viruses (HPV) bacteria (heliobacter)
What are the 4 types of mutations?
Point, substitution, insertion, deletion
What is point mutation?
Changes a single nucleotide within a sequence
What are the 3 types of substitution mutations?
Silent: no change bec of degeneracy (neutral) Missense:1 AA changed = variation (good) Nonsense: stop codon made = shortens PP chain (bad)
What do insertions and deletions cause?
Changes reading frame = diff translation
How is sickle cell anemia caused? (7)
Base substitution in hemoglobin (beta chain) 6th codon (sense strand: not transcribed) GAG = GTG glutamic acid = valine
How does base substitution in SCA cause the sickle shape?
Alters structure of beta chain = insoluble strands which makes hte red blood cell sickle shaped
Why are sickle shaped blood cells useless? (3)
Can't carry O2 properly = anemia forms clots
3 ways species differ in genetic patterns?
Genome size chromosome no gene no
2 ways pros and euks differ
Pros: smaller genomes and fewer genes euks: variety of genome sizes and gene numbers
What is a chromosome?
A double stranded DNA molecule
How do the nucleus of euks and pros differ?
Pros have no membrane bound nucleus have a genophore and plasmid instead
What are 2 features of pro chromosomes?
Not bound by histone proteins more compact due to no introns
Which pro organelles are found in euks? Evidence? (2)
Chloroplasts and mitochondria have plasmid DNA can self replicate
How are plasmids exchanged? (2)
With the sex pili through the process of bacterial conjugation
What are the steps of compacting DNA (7)
DNA nucleosome chromatosome solenoid 30 nm fibre chromatin chromosome
How are homologous chromosomes similar? (2)
Same structural features (size, pattern) same loci positions (Alleles may differ)
What is a karyotype?
A picture of all the chromosomes paired for an individual arranged in size
How are karyotypes formed? (3)
Harvesting fetus / white blood cells chemically induced cell division when mitosis stops
What are karyograms used for?
To determine the gender of a fetus check for chromosome abnormalities
What is non-disjunction? (2)
When chromosomes don't separate properly = extra or missing chromosomes aneuploidy
What is meiosis?
How sex (haploid cells) are made = germline cell = 4 cells
What happens during the two divisions to create 4 haploid cells? (2)
1) separates homologous chromosomes to half the chromosome number (haploid) 2) separates sister chromatids (made from DNA replication in interphase
What does DNA replication in interphase form?
2 genetically identical copies = sister chromatids (1 chromosome)
What are the phases of meiosis? (PMAT)
Prophase metaphase anaphase telephase
Describe the different stages in meiosis I? (4)
P = chromosomes condense, membrane dissolves and crossing over happens with paired chromosomes (bivalents) M= spindle fibres connect to bivalents to align them in the middle A = spindle fibres contract and homologous chromosomes are pulled away to opposite ends T = chromosomes decondense and cell divides to 2 haploid cells through cytokinesis
Describe the stages of meiosis II?
P = chromosomes condense, membrane dissolves M = spindle fibres attach to chromosomes and aligns them in the middle A = spindle fibres pulls sister chromatids away seperating them T = chromosomes decondense, membrane reforms and cell divides to form 4 haploid cells
Why can the 4 haploid cells from meiosis be genetically distinct?
Because of crossing over in prophase 1 can cause recombination
Explain how crossing over of chromsomes work and when does it happen?
Prophase 1 in meiosis homologous chromosomes are paired up to form bivalents held together at chiasmata crossing over happens at chiasmata which can form new combos forms recombinant chromatids
How and where does crossing over occur?
In prophase 1 in meiosis crossing over occurs at the chiasmata which forms recombinant chromatids by exchanging genetic material
How does metaphase 1 lead to more variation?
Due to random independent assortment of chromosomes into the gametes when aligning in the middle
What would happen if the chromosome numbers were not halved?
The total chromosome numbers would double in each generation = polyploidy
What are the 3 ways genetic variation is achieved?
Crossing over in prophase 1 random assortment in metaphase 1 random fusion of gametes
What is non-disjunction? (2)
When chromosomes don't separate properly = extra or missing chromosomes aneuploidy
When can non-disjunction happen? (2)
When chromosomes don't separate in anaphase 1 = affects all 4 when chromosomes dont separate in anaphase 2 = affects 2
How is down syndrome caused?
3 copies of chromosome 21 ( trisomy)
What can influence the chances of non-disjunction occuring?
Maternal age because of developing oocytes being in p1 until ovulation especially after 30 mostly from non disjunction in meiosis 1
What is karyotyping? how is it done?
Chromosomes are organised to find genetic abnormalities cells are harvested from fetus before cell division so that the chromosomes are visible
What is chorionic villi sampling?
Removes placental tissue at 11 weeks to find CS abnormalities 1% risk of miscarriage
What is amniocentesis
Amniotic fluid at 16 weeks to find CS abnormalities with 0.5% chance of miscarriage
What are the differences between mitosis and meiosis? (8)
Division – Mit 1 division mei 2 divisions Independent assortment – Homologous pairs are randomly separated into separate cells only in meiosis Synapsis – Homologous pairs form bivalents in meiosis only Crossing over – Non-sister chromatids of homologous pairs may exchange genetic material in meiosis only Outcome – Mitosis forms 2 cells meiosis forms 4 Ploidy – mitosis forms diploid while meiosis forms haploid Use – Mitosis is used to clone body cells, while meiosis is used to generate sex cells (gametes) Genetics – Cells produced by mitosis are genetically identical (clones), while cells produced by meiosis are genetically distinct
What are the 3 factors that cause mutations?
Radiation - UV from sun, gamma, X-rays chemical: reactive oxygen species (pollutants) biological: bacteria and viruses
What are Mendel's laws? (3)
Law of segregation: alleles separate when gametes form law of independence: alleles separate independently principle of dominance: dominant alleles mask recessive alleles
How did Mendel discover these laws? (3)
Large number of pea plants were crossed 1) crossed a variety of purebred peas 2) crossed the offspring with each other 3) crosses performed again and again for reliable results
How did the results show these laws?
The offspring only expressed 1 allele not a mix (shows dominance)
What are the exceptions of mendel's laws? (2)
Linked genes: genes located on the same chromosome some genes show co-dominance or incomplete dominance
What are gametes? how are they made haploid? (2)
Haploid cells formed by meiosis separated into different nuclei in meiosis 1 separating the allele pairs
What happens to number of alleles when gametes fuse?
Zygote will have 2 alleles for each gene
What is an exception to having 2 pairs of each gene?
Males sex chromosome only have 1 allele for each gene because XY arent paired
What does homozygous mean in terms of genes?
Maternal and paternal alleles are the same
What does heterozygous mean in terms of genes?
Maternal and paternal alleles are different
What does hemizygous mean? and what is considered to be hemizygous?
Male sex chromosomes because only 1 allele for each gene is located on the chromosome
What is genotype? (2)
Gene composition for a specific trait can be hetero or homozygous
What is phenotype?
Observable characteristic of a specific trait determined by genotype and environment
What is codominance
When both alleles are expressed equally Eg: black and white feathers Csmall B CsmallW CBCW
Explain the dominance of ABO blood group
A and B are co-dominant and change the antigen structure O is recessive and doesnt change the antigen structure blood group alleles are represented as I smallA IsmallB or i
How are genetic diseases caused?
Mutations to genes affect cell function
What is cystic fibrosis? (5)
Autosomal recessive disorder mutation to CFTR gene on chromosome 7 produce thick sticky mucus which clogs airways and digestive ducts respiratory failure and pancreatic cysts heterozygous people will only be a carrier